Who played the character part of criminal mastermind 'Fearless Leader' in the film 'The Adventures of Rocky and Bullwinkle'?

"The Adventures of Rocky and Bullwinkle" is a 2000 live action/animated adventure comedy film produced by Universal Pictures, based on the television cartoon The Rocky and Bullwinkle Show by Jay Ward. The animated characters Rocky and Bullwinkle shared the screen with live actors portraying Fearless Leader (Robert De Niro), Boris Badenov (Jason Alexander), Natasha Fatale (Rene Russo), Piper Perabo, Randy Quaid, Kenan Thompson, and Kel Mitchell. Reprising her role as Rocky was June Foray, and Keith Scott voices Bullwinkle and the film's narrator.

The film features an ensemble cast of guest appearances by performers including Paget Brewster, Janeane Garofalo, John Goodman, David Allen Grier, Don Novello, Jon Polito, Carl Reiner, Whoopi Goldberg, Max Grodenchik, Jonathan Winters and Billy Crystal.