Jessica Lange
The OG of surprise casting moves, Jessica Lange's involvement from the start with American Horror Story: Murder House made the world take notice of the ambitious new FX series. The two-time Oscar winner starred in the first four seasons and returned as her Murder House character, Constance, for AHS: Apocalypse.
Emma Robets
Emma Roberts would go on to become a fixture in Ryan Murphy's TV universe, but prior to her introduction in American Horror Story: Coven, her TV work was more kid-friendly. A role in Scream 4 would change her trajectory.
Lady Gaga
When Jessica Lange left, Ryan Murphy and Co. went the other direction and brought in Lady Gaga for American Horror Story: Hotel. This was Gaga's first major acting gig where she wasn't playing herself aside from an uncredited role in a 2001 episode of The Sopranos. After AHS: Hotel, she appeared in AHS: Roanoke.
Billy Eichner
Known for his comedic stylings, specifically his series Billy on the Street, Billy Eichner went serious for American Horror Story: Cult. He also appeared in American Horror Story: Apocalypse.
Gus Kenworthy
For the younger-skewing slasher/ghost season American Horror Story: 1984, Ryan Murphy and Co. tapped Olympic skier Gus Kenworthy for his first acting role where he wasn't playing himself.