In Ice Age: Dawn of the Dinosaurs, the giant weasel who helps rescue Sid is Buck.
Buck is an eccentric, one-eyed weasel who lives in the dinosaur world beneath the ice. He becomes Manny, Ellie, Diego, and their friends’ guide when they enter that hidden environment to find Sid.
Buck is not the villain of the film. The main danger comes from the dinosaur world, especially the enormous predator Rudy. Buck’s knowledge of the underground jungle and his long-running rivalry with Rudy make him essential to the rescue mission.
The character became one of the series’ most popular additions and later received a Disney+ spin-off, The Ice Age Adventures of Buck Wild. Simon Pegg provides Buck’s voice in the theatrical film.