- "I love you, son."
- ―Caesar and Cornelius reunited.
Cornelius is an evolved common chimpanzee, the youngest son of the late Caesar and the late Cornelia, and the younger brother of the late Blue Eyes. Through his father, Cornelius is the youngest grandson of the late Bright Eyes, and the late Alpha, as well as the youngest adoptive grandson of Will Rodman and Caroline Aranha, and the youngest adoptive great-grandson of the late Charles Rodman. He was second-in-line to inherit the colony after his older brother.
Following the deaths of his parents and brother, Cornelius is now the sole heir to Caesar's throne.
Dawn of the Planet of the Apes
One day following the decade the apes left the city and thrived in the Muir Woods, Caesar returned home from a hunt to learn his wife Cornelia is in labor. Caesar rushed to his tree just in time to be by Cornelia's side as she gives birth, which came with complications unlike with Blue Eyes' birth, to their newborn baby boy. The baby, later named Cornelius, cried as he gasped his first breath and placed in his mother's arms. His father and mother gazed at him with happiness, then turned to see his elder brother, who was scarred by a wild bear, enter the tree to see his newborn brother as their parents continued to touch Cornelius so he can know they were his parents.
Having just been born, Cornelius slept most of the time with his mother, who was developing complications after the birth. One day, Cornelius and his mother slept as a gunshot was heard throughout the woods, which woke Caesar, who investigated with a large troop of apes and discovered a group of humans standing in front of Blue Eyes and Rocket's son Ash, who was shot by one of the humans.
The following night after Caesar made a deal with the human group, consisting of Malcolm, Ellie, Alexander, Carver, Forest and Kemp, he returned to see Cornelius sleeping while Cornelia was wheezing, which concerned Caesar but she assured him she just needs rest. Caesar then gazed at Cornelius as he worried the humans presence can place him and the tribe in danger, which Cornelia picked up. By sunrise, Caesar and Blue Eyes took Cornelius, so Cornelia could rest, and made it to the hydro dam site as Malcolm's group began their work to fix it and restore power to the ruins of San Francisco. Joining Rocket and the orangutan Maurice, Caesar and Blue Eyes, who was holding Cornelius, stood watch until Caesar noticed the bonobo Koba wasn't present. Cornelius, wide awake, observed his surroundings while in his brothers arms.
During their work, Malcolm's group set off an explosive to clear the dam's interior, which trapped them at the same time. Rocket, Ash, and a gorilla named Luca went in the dam and saved them, bringing them back outside so Ellie can treat Carver and the rest clean themselves from the dirt. Cornelius became intrigued by the humans' presence and leapt out of his brother's arms as Malcolm told Caesar gratitude and explained what else his group needs to do. Cornelius crawled up Ellie's back to get a better look at them before moving in front of Alexander's knee. He looked at both Ellie and Alexander, who began to connect with the young ape until he moved to the ground and examined Alexander's shoe before heading to an open case. As he sat rummaged through the case's contents, he unveiled a shotgun, which Carver kept hidden as the deal between Malcolm and Caesar was the group can stay if they surrendered all the guns in their possession. Carver, who spotted Cornelius, jumped up and yelled at Cornelius to get out of the case, which angered Blue Eyes and forced him to tackle the human. Cornelius got out of the case and ran to cover as Blue Eyes kept Foster and Kemp at bay as they tried to get Carver out, who reached for the gun and pointed it at Blue Eyes, shocking everyone until Caesar disarmed Carver. Sensing their unintended deception, Caesar tossed the gun in the lake and grabbed Cornelius as he ran towards his father, who yelled at Malcolm to leave.
Returning to their village, Caesar and Blue Eyes were approached by a panicking Sparrow, one of Cornelia's midwives, who revealed to them Cornelia has gotten worse. Caesar and Blue Eyes, holding a sleeping Cornelius, ran into their tree to see Tinker and a midwife by Cornelia's side, who's breathing has worsen and became unresponsive. Both Cornelius' father and brother stood by Cornelia's side until Rocket brought up Malcolm and Ellie, who apologized and struck a new deal: Ellie will help Cornelia with antibiotics and Caesar will allow Malcolm's group to stay, but for one day and to have Carver kept far away from the apes while they help Malcolm's group repair the dam, which angered Cornelius' brother.
The next night, Cornelius' mother made a full recovery and came out of Caesar's tree with Cornelius in her arms. Caesar, who allowed Malcolm's group, excluding Carver, to enter their village and see the lights in the city come back on as they have fixed the dam and restored the power, went up to her and they embraced before taking their infant son to gaze at the lights. Standing near a cliff on the right corner of the tree's roots, Cornelius stayed with his mother as she went to Blue Eyes, who hugged her in happiness to see her well until Caesar was shot, by Koba lurking in the darkness after having been humiliated by Caesar and deemed him caring more for the humans than his own kind, and fell over the cliff. Cornelius was startled as Cornelia and Blue Eyes called out to Caesar, then the entire village began to burn, which was caused by Stone. After Koba came and lied that the humans killed Caesar and set their home on fire before declaring war on the humans in the city, he decreed that the females and children stay in the woods while the males head for the city.
Two nights later, Cornelius and Cornelia headed for the city as Koba summoned them after defeating the humans. By sunrise, all the females and children made it to the colony, an unfinished building where the surviving humans were living, and learned that a few apes died from an explosive set off by the colony's leader in a suicide. Blue Eyes found Cornelius, who was in slumber, and their mother and brought them to Caesar, who survived Koba's attempt. Cornelius' father, mother and brother embraced one another before Caesar reasserted his dominance over the tribe and made preparations for war as Malcolm informed Caesar that a military group is coming to San Francisco.
War for the Planet of the Apes
Cornelius, now two, has learned the concept of war as his tribe continues the fight with Alpha-Omega for the last two years while seeking refuge in a secret cavern system hidden in a waterfall. One day as his father returned home with a troop of wounded apes, Cornelius walked with his mother Cornelia, who was shocked and happy to see Blue Eyes and Rocket, who have returned from their journey of finding a new home for the tribe. As Cornelia hugged her oldest son, Cornelius hurried over to his father, grabbing him by the hand as he didn't remember his own brother due to his absence over the two years, and hesitated to say hi as Blue Eyes turned to greet him. Their mother help remind Cornelius of Blue Eyes as Caesar lifted him up and cradle him, allowing Cornelius to greet his estranged brother nervously before their mother directed Blue Eyes to his mate Lake. As Blue Eyes and Lake embrace each other, Cornelius watch his father cradle his mother as both parents are happy to see their son returned safely.
In the evening, Cornelius stayed with his mother as she partook a council with his father, Blue Eyes, Lake, Rocket, Spear, the orangutans Maurice and Percy, and the gorillas Luca and Winter, the sole albino in the tribe. Cornelius examined a map his elder brother presented with curiosity as he explained it leads to their new home: an untouched oasis hidden by a chain of mountains. Cornelius was then dragged back close to his mother before she asked Blue Eyes what lied beyond the mountains as Cornelius grabbed her leg. Blue Eyes grabbed one of the satchels from Rocket and pulled out sand, which Cornelius attempted to take some from Lake's hand, and Blue Eyes revealed a vast desert lies beyond the mountains, which as as the perfect cover to keep humans from searching there for the tribe. Cornelius then drifted into sleep as Winter argued to have the tribe leave tonight, but Caesar and Blue Eyes decreed they're not ready and moving now would place the entire tribe in jeopardy, and Caesar assured all the apes they will leave the woods safely as long as they remain together.
Later that night, Cornelius, sleeping with his mother and brother as his father stayed up to examine the map, made a hoot in his sleep, which made Caesar rub his sleeping son's head. Cornelius and Cornelia were then woken by his brother, who revealed that danger has come. Cornelius and his mother stood behind Blue Eyes as he spotted a female soldier emerging from a cavern below their nest. Cornelia kept Cornelius low as the soldier made her way around the rock pillar supporting their nest, leaving her expose for Blue Eyes to tackle her to ground before he beat her to death as Cornelia concealed Cornelius in a hiding spot deep in the rock pillar's base in the backside. As he remained still, Cornelius watched in horror as gunshots erupted the large cavern's base, followed by his brother and mother falling close to the female soldier's body, both dead, traumatizing the young ape. Horrified, Cornelius remained still as the killer talked over his radio that the apes' leader is dead, and Cornelius did nothing to see what happened next: which unknown to him, his father returned to the opening to see the killer, Colonel McCullough, preparing to leave and his wife and eldest son dead, enraging Caesar to go after the killer, followed by more apes emerging from one of the tunnels.
As the group of apes, with Luca, Spear, Rocket and Maurice left to search for Cornelius, who, to them, was unaccounted, leaving a devastated Caesar staring at the scene of his family's death. Hearing his father breathing angrily, Cornelius decided to reveal himself, which his father was relieved to see him alive and opened his arms, and Cornelius ran to him and hugged him, crying in sorrow while Caesar assured him he's safe.
In the morning, Cornelius walked with his father among the tribe, that was preparing to leave due to their refuge compromised, on the lake's shoreline. Caesar approached a grieving Lake and charged her with looking after Cornelius because he's not travelling with the tribe to the oasis. Cornelius whimpers to his father not to leave, but chose to obey his father as he walks to Lake's side. He then watched Maurice talk to Caesar, who realized he's going after the soldiers, but Caesar revealed that he's going to hunt down the Colonel to kill him, which Maurice told Caesar the tribe can't leave without him. Caesar told Maurice they have to as the soldiers could return in full force. Cornelius, crying, called to his father while Lake attempted to calm him; Caesar then revealed he plans to divert the soldiers away, leaving the whole tribe a chance to leave the woods before leaving. Cornelius cried with the tribe as Caesar disappears in the woods, followed by Maurice, Luca and Rocket as they chose to accompany him.
Much to the their horror as they made their way out of the woods, the tribe was intercepted by Alpha-Omega and were prepared to kill the apes until the Colonel stopped them and had all the apes brought back to their base on a Californian border up north. Once the tribe was brought into the soldiers' base, a former weapons silo that was used for a relocation facility during the Simian Flu epidemic. Cornelius and the other ape children were separated from the adult apes as they were forced to build a wall. Days later, Cornelius was shocked to see his father, who found the Colonel's base and was horrified to see his tribe was captured, brought toward the adult apes' pin in chains by the Colonel himself, a soldier, and a Donkey. Cornelius called out for his father, which caught the Colonel's eye, who was unaware Caesar still had one more son. Caesar didn't show his son acknowledgment, since he wanted to protect him from death and the Colonel dismissed it and had the solider and Donkey place Caesar in the pin. After they left, Cornelius cried and called out to his father, attempting to reach for him through the bars.
The next three days, Cornelius and the other children watched as the soldiers and Donkeys terrorize force the adults and force them to work, until one day Caesar, Rocket and Maurice, who were hiding outside of the base, concocted a plan to free the apes and leave the base, as Caesar discovered that an army from the north is coming to fight against Alpha-Omega. On the third night, Caesar and Rocket managed to acquire the key to the pins and slip into the children's pin, as the tunnel they dug underneath began to flood, and began to gather them. As Cornelius woke up, he turned to see his father, bruised and scarred, standing and embraced him, happy to reunite with him. Caesar and Rocket lead the children apes to climb on the wires above the pins, high enough from the soldiers' sights, and jump down into the adult pins, with Cornelius clinging to his father's back as he and Rocket made their way back in the adults' pin and to the hole in the ground. Cornelius was the first to be brought down by Maurice, who was assisted by a mute human girl and a talking chimp, and lead through a tunnel underneath the base and outside.
As the majority of the children were lead to the woods near the base, the northern army arrived and opened fire at the base. As dawn approached, Cornelius, with Lake, Maurice and the girl named Nova, watched as the opposing human armies slaughter one another until the base exploded, allowing the northern army to infiltrate the base. Cornelius wondered where his father was until he and all the children apes were instructed by Maurice, who noticed an avalanche caused by the explosion, to climb the trees. Holding on to a tree with Lake, Cornelius braved the avalanche until it stopped, burying the entire base and killing both the norther army and Alpha-Omega survivors. Cornelius turned to Rocket's hooting to see his father alive and hanging on a tree, who was also relieved and happy to see the remaining members of his tribe alive.
Days after the tribe left the base and resumed their journey, Cornelius, in his father's arms, bared witnessed at the sight of the oasis and all the children and adult apes began to walk towards it. Cornelius spotted Nova, who looked at him, and hid by his father's side nervously until he gestured him to go to her, which he did and walked with her with the talking chimp Bad Ape, who joined them. Cornelius then warmed up to them and played with them, looking to his father with happiness and resumed playing, unaware his father was dying from a mortal wound and paid no attention as the tribe became aware of his passing by Maurice's cries.
Dawn of the Planet of the Apes
As an infant, Cornelius is closely watched by his family, especially his protective older brother, Blue Eyes. Despite his protective family, this doesn't stop Cornelius from exploring and being curious. When his father rescues Malcolm, his family and Carver from an explosion, Cornelius and Blue Eyes are present when Caesar along with their honorary uncles, Maurice and Rocket meet up with the humans. Cornelius becomes curious and wanders over to Ellie and Alexander and investigates them for himself but finds something more interesting; the humans' box of supplies. Cornelius is almost injured but is rescued from the incident by Blue Eyes who attacks Carver for wanting to harm his brother.
War for the Planet of the Apes
Now two years old, Cornelius no longer possesses his curious nature from infancy, as he is now timid and shy, which is evident when he holds Cornelia or Caesar's hand when walking.
- Genius-Level Intellect: As the son of an evolved ape and an altered ape, Cornelius has a high level of intelligence; because his parents inhaled the ALZ-113 early in their life, Cornelius has a higher level of intelligence than both of his parents combined. Cornelius, along with his older brother Blue Eyes, is the most evolved ape in the entire San Francisco Ape Colony.
- Speech: As the second son of an evolved chimpanzee and an altered chimpanzee, Cornelius was born with the ability of speech, while his father (and presumably his mother) learned to speak later in life. In War, Cornelius only spoke through the use of Sign Language, however, considering the fact that he is still two years old, it is likely that he is unable to speak yet.
- Sign Language: In War, now two years old, like his fellow apes, Cornelius knows American Sign Language. He was taught by his parents and his honorary uncle Maurice.
- Like his parents, but unlike his older brother, Cornelius has green eyes.
- Cornelius and Blue Eyes do not seem to possess the shooting star birthmark their father and paternal grandfather hold.
- Cornelius is named after Roddy McDowall's and David Watson's Cornelius I and Bobby Porter's Cornelius II from Planet of the Apes, Beneath the Planet of the Apes, Escape from the Planet of the Apes, and Battle for the Planet of the Apes.
- Cornelius was mentioned at Comic Con 2013 by Andy Serkis and director Matt Reeves, but without his name.
- Cornelius was mentioned again by Andy Serkis during an interview at CinemaCon. One of the scenes shown at the Fox screening was the festivities involving Cornelia, seen wearing a crown of flowers, having just given birth to this child.
- Until the release of War for the Planet of the Apes: Revelations, Cornelius went under the name Milo. During that period, there was speculation from one entertainment site that this infant's name could be Cornelius. Another site has suggested the name Milo and that the baby could be considered the equivalent to Roddy McDowall's Caesar when he was born as Milo in Escape from the Planet of the Apes.
- It was confirmed by Andy Serkis in an interview with USA Today that the baby was a boy
- In the over-all Planet of the Apes franchise, Cornelius' birth is the third recorded ape infant. The first was Milo (later known as Caesar), who was born in Escape from the Planet of the Apes. The second was Milo's father, Caesar, who was born off-screen in Rise of the Planet of the Apes.
- Nick Thurston revealed on Facebook that there was a joke on set that Andy [Serkis] came up with that the baby's name was Will, named in honor of Caesar's adoptive father, Will which served as an on set Easter egg for the cast.
- Cornelius is also the first Chimpanzee sibling to appear in either of the two film franchises.
- Dawn of the Planet of the Apes (novelization)
- War for the Planet of the Apes: Revelations
- War for the Planet of the Apes (novelization)
- War for the Planet of the Apes (BOOM! Studios)