Mr. Big is a significant character in the animated film 'Zootopia.' He is an arctic shrew who is the most feared crime boss in Tundratown, controlling an expansive criminal empire. Despite his small size, Mr. Big commands great respect and fear among Zootopia's underworld due to his influential and powerful status. He is known for his calm demeanor and strict adherence to loyalty and respect. Mr. Big plays a crucial role in the storyline, helping the protagonists, Judy Hopps and Nick Wilde, by providing vital information that aids in solving the central mystery of the film.