James MarsdenThe cast list for Quentin Tarantino's "Once Upon a Time in Hollywood" just keeps growing.

The latest to sign on: "Westworld"s James Marsden and Julia Butters, who plays Anna-Kat in the ABC sitcom "American Housewife." Since it wasn't announced who roles they'll be playing, we might assume they'll be original characters.

We learned late yesterday that Al Pacino will play Marvin Schwarz, the agent to Leonardo DiCaprio's cowboy actor.

Recent additions to the cast include "Homeland" star Damian Lewis as action icon Steve McQueen, Dakota Fanning as Manson follower Squeaky Fromme, and Emile Hirsch as Manson victim Jay Sebring.

The film, which is set in Hollywood right before the Manson murders, will focus on Rick Dalton (DiCaprio), a former star of a western TV series, and his longtime stunt double Cliff Booth (Brad Pitt).

So it's possible that Marsden might be playing yet another cowboy character. (Odds on him turning out to be a robot? Low.)

Since a chunk of the movie is about western TV shows, it seems likely that Luke Perry's already announced character of "Scotty Lancer" was a main character on a real TV show called "Lancer."

Margot Robbie will play the Manson family's most famous victim, Sharon Tate, who also happens to be Rick Dalton's neighbor.

At last report, Tarantino was still looking for someone to play Bruce Lee.

[Via THR]