Oak is an evolved gorilla who served in Caesar's Gorilla Guard.
Biography
Background
Oak was raised in captivity at the San Francisco Zoo by an orangutan named Kumang because Oak never knew his parents. Oak was seven when Buck freed the apes from the zoo during the Ape Rebellion and Oak hung from Kumang as she swung from the treetops. Oak marveled at the beauty of the flowers blooming in the trees even during the chaos and forest fire that happened as the human tried to capture and kill them.
Oak grew up in Caesar's new colony and when he was old enough he joined the Gorilla Guard under Luca. After Koba's betrayal and Caesar's return to power, Oak fought against a human warship on the beach under Ajax, Luca's second in command. Alongside a troop of chimpanzees led by Branch, they succeeded in driving the ship back after Oak and Ajax fired rockets at two of it's cannons. Caesar said they did good, but Oak began to doubt him seeing all the apes that died in the battle, including Branch. Red, a fellow member of the Guard, approached him not long after and convinced him to betray Caesar.
War for the Planet of the Ape: Revelations
Oak later left with the rest to protect the women and children apes while Caesar's Army fought Colonel McCullough's forces. Oak relieved Winter just after sundown and later helped Red disarm him and the other members of the Guard who didn't support Koba. Ajax, second-in-command of the Guard behind Luca and Ursus awoke discovering what they were doing and tried to fight back. Oak and his allies killed Ursus and severely injured Ajax. Oak stood watch over all the disarmed members of the guard alongside several chimps brought in by Grey, the alpha of Koba's Loyalists.
Red later sent Oak out to find Ajax when the initial scouts chasing him did not return. Oak came upon Ajax who was dead alongside the scouts Flint and Shell. After hearing Shell's dying words with Cornelia, Oak grew ashamed of his role in the coup and threw his gun to the ground. Oak said "ape not kill ape" and knelled at Cornelia's feet, showing he was now loyal to her and Caesar again. The next day, after Cornelia expressed her wish to return to the rest of the females with Grey and Red, Oak and another chimp, Maple, offered to accompany her. Cornelia first asked Oak to leave his rifle, which he had picked back up, behind before they left and Oak threw it back on the ground without hesitation, growing to hate them.
Oak, Cornelia and Maple approached Winter hoping to get by him when he raised his rifle and pointed it at Cornelia. Oak tried explaining to Winter that Red lied to him about Cornelia being a traitor and was part of a plan to usurp Caesar, but Winter was too confused to know who to believe. Oak stepped in front of Cornelia and Winter's gun, shielding her from harm, and told Winter he wouldn't harm the queen. Cornelia told Oak to let her through and despite Oak's protectiveness, Cornelia manages to convince Winter to let them pass, Oak giving Winter a fierce look as he passed Winter.
When Red attempted to kill Cornelia as she was helping a chimpanzee named Rain give birth, Oak is the first ape to step between Red and Cornelia before the female apes joined him. After Grey defeated Red in battle he ordered Oak to release the members of the Gorilla Guard they had tied up before Grey is shot in the head by Red. Red attempted to shoot Oak as well before he realized his gun had jammed and the female apes attacked him, chasing Red away.
Faithfully Service to Caesar
Oak served Caesar faithfully again and accompanied Spear and Barbar on Caesar's orders to find a place Koba and Grey had found while scouting. While out exploring they found a system of caves obscured from vision by a waterfall. They returned to Caesar, exhausted but excited, and told him the good news so they could relocate there. Oak eventually managed to reach the oasis that would become their new home and told Maurice stories about his life so he could write them in a book Maurice planned to give to Cornelius when he was old enough.