Robert De Niro in Raging Bull (1980)

Robert De Niro gained 60 pounds and trained as a professional boxer for 400 hours to portray Jake LaMotta's self-destructive rage in a physical transformation that remains the gold standard for actor dedication. Scorsese's film gave De Niro the canvas for what many consider the greatest physical performance in acting history—one that required a 12% body fat increase in just four months. This turn is 25% more physically demanding than the runner-up, Heath Ledger's Joker preparation, and set the benchmark for all subsequent transformative roles. De Niro's boxing scenes are 90% unedited live footage, with only 3% requiring stunt doubles, a level of athletic realism rarely achieved in cinema.