18. Robert Downey Jr.
To know Downey today, it’s hard for (especially younger) audiences to remember that once upon a time we all braced for his early death. Downey played a crack addict in the 1987 movie, Less Than Zero. What we would later learn is how that movie portrayed Downey’s real life struggles with addiction. At one point he was so gaunt from cocaine abuse, a strong breeze might have blown him away. He recovered, obvi. For Iron Man, Downey gains about twenty pounds of lean mass every time he dons the suit.