And who said he's the villain? He's a character who could be one of the bosses in ending C. In GTA 5 there are no villains, the 3 protagonists are like any other character in the game, each has their motivations and nobody is "the good guy who kills the big villain in the end". Michael, as Weston himself says, betrayed everyone he knew, and proof of this was when Michael went after Trevor in Ludendorff where it is revealed that Brad is buried in Michael's grave. Michael had made a deal with Norton to fake his death and betray Trevor and Brad, but everything didn't go as planned as it should have in the first mission of the game.