The weasel voiced by Simon Pegg in Ice Age: Dawn of the Dinosaurs is Buck.
Buck is an eccentric one-eyed weasel who lives in the dinosaur world beneath the ice. He acts as a guide for Manny’s group after they enter that environment while searching for Sid. Buck is brave, highly energetic, and unusually knowledgeable about the dinosaurs and terrain.
Simon Pegg’s performance gives Buck a fast-talking, adventurous personality that contrasts with Manny’s caution and Diego’s more controlled attitude. Buck’s obsession with hunting the dinosaur Rudy also supplies one of the film’s major personal storylines.
Buck later returns in Ice Age: Continental Drift and becomes the central character of The Ice Age Adventures of Buck Wild. He is sometimes confused with Crash, Eddie, or Louis, who are other supporting characters in the wider franchise. Buck is specifically a weasel, not a possum or molehog.