Sid

Sid's family leaves him behind in the migration. He decides to follow Manny, the mammoth who saves him from two brontotheres, and insists on staying even against Manny's wishes. Sid looks after the human baby with Manny and Diego, and the three become friends.

In the second film, Sid invites Ellie and her brothers Crash and Eddie to join the trek to the boat. At the end he revives Scrat after the fall into the crack, and gets attacked for it.

Afraid of being alone, Sid finds three eggs and decides to look after them, against Manny's orders. The eggs hatch into three baby T. rexes. When their mother carries them off to the lost world, Sid goes along. He grows attached to them and, in the end, says goodbye.

Sid's family comes back only to drop off Granny and leaves again. Sid, Granny, Manny and Diego drift away on an ice floe and fall into Gutt's pirates' hands. Sid and Granny end up on an island with the herd.

Sid is about to propose to his girlfriend, but she dumps him. In Geotopia he meets Brooke, a sloth who falls for him at once. He wrecks the city by accident while trying to take a crystal as a gift. In the end she shows up at Peaches' wedding.

In the Christmas special, Sid knocks into Manny's family Christmas Rock and shatters it. Manny puts him on the Naughty List, and Peaches takes Sid to the North Pole to prove Santa is real.

John Leguizamo voices Sid. According to Wikipedia, Sid was originally a con artist, and a finished scene had him scamming aardvark kids. The studio changed him into a talkative klutz because it felt audiences would dislike the earlier version.