In 1968's Planet of the Apes, Cornelius is introduced as the fiancé of Dr. Zira, an animal psychologist and veterinarian, both of whom are on the scientific staff of Dr. Zaius.

In Beneath the Planet of the Apes, Cornelius and Zira meet another astronaut, Brent, who appears at their doorstep after being shot by a gorilla.

Zira gives birth to Milo (renamed Caesar in Conquest of the Planet of the Apes ) and is taken into hiding by Armando, a sympathetic circus owner.

After being discovered by Dr. Hasslein, Cornelius and Zira escape with a normal chimpanzee baby, which they had switched with Milo to ensure his safety.

Cornelius first appeared in 1963 in Pierre Boulle's novel La Planète des singes (known in English as Planet of the Apes).

During a 1966 makeup test for the original film, actor James Brolin portrayed Cornelius, alongside Linda Harrison (later to play Nova) as Zira and Edward G. Robinson as Dr. Zaius.

Caesar, in both Battle for the Planet of the Apes and the reboot trilogy, has a son named Cornelius in honor of McDowall’s character.