Mr. Big is a gray arctic shrew with a pink nose, pink feet, pink paws, black hair, heavy black eyebrows covering blue eyes, a black suit with a red boutonnière and black bow tie, white spats and an emerald green ring on his right pinky. Despite being called Mr. Big, he is small in size.
Mr. Big is merciless, sophisticated, fearsome, family-oriented, and protective. Despite being a crime boss, Mr. Big is not completely villainous since he has good intentions as he is nice to the protagonists, Judy Hopps and Nick Wilde. Mr. Big also commands respect, and when he feels disrespected, he is willing to kill anyone who disrespects him.
As a child, Mr. Big was raised by his grandmother, whom he loved and respected dearly. Mr. Big's grandmother, or "Grandmama", was responsible for teaching Mr. Big the values of respect, determination, and family. In The Official Zootopia Handbook, it was revealed that Mr. Big had humble beginnings, but grew to become a successful business owner, starting with a tuxedo rental shop, and later grew a family for himself, cherishing his daughter Fru-Fru.
It was also revealed that Nick Wilde once had a history with Mr. Big as they once developed a partnership and one that Mr. Big valued due to Nick's suave reputation as a con artist. However, this partnership was short-lived when Nick took advantage of Mr. Big by selling him a very expensive wool rug made from the fur of a skunk's butt. Mr. Big developed a sincere grudge against Nick following this event as it disrespected the former and his grandmother, who passed away shortly after this. As such, Mr. Big angrily told Nick to stay away or he would be killed the next time they meet again.
Mr. Big first appeared when several of his Polar Bear Thugs (Raymond and Kevin) brought in Nick and Zootopia PD officer Judy Hopps, who were caught snooping around Mr. Big's limo following the disappearance of Mr. Otterton. At first, Mr. Big attempt to have both Nick and Judy killed, but his daughter Fru-Fru recognized Judy as the officer who saved her from a crushing donut statue. Because of this event, Mr. Big decided to spare Nick and Judy for the moment. During Fru-Fru's wedding, Mr. Big explained to Nick and Judy that he sent the limo to Mr. Otterton as the latter wanted to discuss business with him, but something went wrong during mid-journey. Nick and Judy soon learned that Otterton and the limo driver Mr. Manchas went savage along with 10 missing predators, and that they were illegally detained by Zootopia Mayor Lionheart.
Following Lionheart's arrest, Judy soon learns that the cause the predators' savage was due to a rare flower called the Night Howler. Knowing that Duke Weaselton tried to steal a few Night Howlers for money, Nick and Judy take Duke to Mr. Big, informing the latter that Duke was the one who kicked the donut statue that almost killed Fru-Fru in the first place. With this information, Mr. Big demanded Duke to talk by threatening to ice him, and a frightened Duke admitted that he wanted to sell the flowers to a ram named Doug Ramses, who's creating serums out of the flowers to make predators go savage as part of Dawn Bellwether's plot to create a prey-supremacist society in Zootopia. It also turns out that both Otterton and Manchas were shot with the serum along with the other predators as part of Bellwether's plot that made them go savage in the first place.
Following the arrest of Bellwether and her cronies for their crimes and the savage animals being cured, Mr. Big is last seen attending a concert (hosted by Gazelle) along with Fru-Fru and Koslov, happily enjoying Gazelle's singing voice.
Mr. Big is inspired by Vito Corleone from The Godfather series, hence his appearance and mannerisms.