Hugh Jackman in X-Men Origins: Wolverine, The Wolverine and X-Men Days of Future Past
You want a classic buff-up guy? Check this guy out: Hugh Jackman. The actor, who has played as Wolverine since X-Men came into the big screen, bulked up quite a lot for his role over the years but it was in the X-Men Origins, The Wolverine and X-Men Days of Future Past where it showed he bulked WAY up for his role. Wolverine is known to be a muscular and agile mutant with claws so Jackman had to bulk up to portray Wolverine right.
And you know how serious he can be about this? He once tweeted an image of himself during Days of Future Past filming time deadlifting to the point that the bar bended and he said that “if the bar ain’t bendin’, you’re just pretendin'” Well then, guys, you heard the mutant, stop pretendin’ and get that bar bendin’!