Cornelius lived in the newly built Ape City with his family and friends, including both apes and humans. He was enthusiastic about shared peace between humans and apes, and was his father's number one supporter. Cornelius thought highly of Abe the Teacher and in good gesture, he knowingly changed his writing of Ape to Abe so that it read as: "Ape shall not kill Abe". As a young chimp, Cornelius preferred to play with his young human friend, especially war games with pretend guns, even though he was scolded not to do so by his mother.
One night, his pet squirrel escaped from its cage, so Cornelius crept out of his parent's sight to go after his pet. After overhearing General Aldo and the gorillas planning to overthrow Caesar, he was caught eavesdropping on them and was chased up a tree. Afraid about losing the secrecy of his plans, Aldo then cut the branch Corneilus was standing on with his machete, leading to the prince falling towards a fatal injury to his death. Cornelius was treated back at home as he tried to tell Caesar about Aldo's plans, but nothing could save him from dying in bed. Caesar and Lisa wept over the loss of their son in the midst of the "Battle for the Planet of the Apes", but Aldo's attempt on their son's life was exposed and they cornered the gorilla general up a tree, chasing him towards the same fate he put on Cornelius. Unlike Cornelius, Aldo died from his fall straight away and was avenged for breaking the "Ape shall not kill Ape" law.
- The Power Records adaptation of Battle made no reference to Cornelius, instead using Aldo's attempt to seize power as the spark for his climactic fight with Caesar.
- Cornelius plays "war games" with a human child on-screen. In a script, this friend is called "Jimmy".
- Cornelius' pet squirrel was called "Ricky".
- Cornelius was named in honor of his paternal grandfather; even though Caesar never knew him.
- In an early draft treatment for Battle, Caesar's infant son is given the full name "Cornelius Armando", and is born in 2004.
- Cornelius was played by Bobby Porter who reappeared as two different characters in the following year's TV series - Arno and Remus.
- In the second reboot film of the franchise - Dawn of the Planet of the Apes - Blue Eyes, the son of Caesar and Cornelia, shares similarities to Cornelius.
- As a reference to Cornelius' death in Battle for the Planet of the Apes, the reboot franchise's film, Dawn of the Planet of the Apes, played on this plot point with the death of Caesar's (Andy Serkis) honorary nephew Ash being the catalyst for Caesar's fight with Koba as a way of avenge the young ape's death. Koba, much like Aldo, falls to his death. The scenario was similar to that of Battle, where Caesar fights Aldo and avenges his son's death.
- Also in the reboot franchise, Caesar and Cornelia's second son is named Cornelius, supposedly having been named after his mother.
- Battle for the Planet of the Apes (novelization)
- Planet of the Apes Magazine: Battle for the Planet of the Apes