Often times I read a story where one character is developed and another character is nearly invisible. All major characters should have a hint of personality. (Unless of course it is their dullness which you wish to emphasis.) Even the most trivial and fleeting of random bit players should not be just ordinary folks. Example: a waitress with a hawk nose or bright red fingernails.
Special Note: If a story has a narrator, this is a major player and their character should emerge, slowly, methodically and evenly throughout. REF: The Great Gatsby.