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 will be second-in-line to inherit the colony after his older brother, Blue Eyes.
Following the deaths of his father and brother, Cornelius will succeed as the next Ape King.
Dawn of the Planet of the Apes
Born before the rediscovery of humans, Cornelius was born the second child and youngest son of ape king, Caesar and his queen Cornelia. Through his parents, he is the younger brother of the couple's heir and eldest son, Blue Eyes.
When Caesar rescues a group of humans consisting of Malcolm, his wife Ellie, his son Alexander and Carver, Cornelius along with his brother meets humans for the first time. Curious, Cornelius climbs out of Blue Eyes' arms and scurries over to Ellie and Alexander to investigate them further and to play with them much to the nervousness of his older brother and the amusement of Alexander and Ellie who take his curiousness and playfulness in stride.
Cornelius's playtime came to an all too soon halt when he started to take a look inside Carver's supply box for a new toy and uncovered a hidden shotgun. Carver rushed over in fear to recover his property and was set on attacking the innocent baby chimp if not for his protective older brother. After a tense moment of betraying and the attempt on his sons lives, Cornelius quickly returned to his father's arms and was escorted home where he remained in his mother's care for the remainder of the human's venture and Koba's rebellion.
Cornelius is later seen asleep in his mother's arms at the time he is reunited with his father and brother after Koba is announced dead and is present when his father prepares his army for war with the humans.
War for the Planet of the Apes
Cornelius is seen with Cornelia at the beginning of the film when Blue Eyes returns, and Caesar tells him to "say hi to his brother." He is later shown sleeping in Cornelia's lap during the ape council meeting. At night, when Cornelia and Blue Eyes are murdered by the Colonel, Cornelius hides. While the other Apes look for him, he makes himself known to a distraught Caesar who is sitting where his wife and son's bodies had been found.
Caesar leaves Cornelius in the care of Blue Eyes' mate, Lake as he goes off on his journey, Cornelius screams his name as he goes off. Later at the labor camp, Cornelius cries and calls for Caesar when he is brought in.
When the apes escape, Caesar picks up Cornelius and tells him he loves him. He rides with Caesar away to the Apes' new home. He is presumably raised by Lake after Caesar's death.