In the opening scene of Michael Winterbottom's Tristram Shandy: A Cock & Bull Story, Rob Brydon argues that the movie is a co-lead. In the next scene, Steve Coogan, as Tristram Shandy, argues that he is "the main character in this story, the leading role." The rivalry continues throughout the film. We don't get to see it, but Rob Brydon, as Uncle Toby, will ultimately have the larger role since both his battle scene and his time with Wadman are to be included.
Although Tristram is a constant narrator in Laurence Sterne's The Life and Opinions of Tristram Shandy, Gentleman, his presence as a character is almost nil. Uncle Toby is the larger.