Jared Leto
Once more, Jared Leto finds himself on this list. Not because of his capability for extreme weight loss in short periods of time, this one exemplifies his ability to put on massive amounts of weight in anticipation of a role. This movie is called Chapter 27, in which Jared Leto plays Mark Chapman, the man who assassinated John Lennon.
Making a Murderer
Leto is, what industry folks call, a method actor. He lives like, acts like, and refers to himself as the name of his characters for long periods of time prior to actually playing them on camera. In this particular instance, his depiction of Mark Chapman caused him to gain 67 pounds in three months.