Herriman, best known for having a recurring role on FX's Justified, will be taking on the role of Manson as the film takes place in Los Angeles during the summer of 1969 when the Manson Family murders took place.
Ronin will be portraying Polish actor Voytek Frykowski, who was one of the victims of the Manson Family murders which took place at filmmaker Roman Polanski's home. Actress Sharon Tate, another victim and former wife of Polanski's, will be portrayed by Margot Robbie.
Once Upon a Time in Hollywood, set to arrive in theaters on July 26, 2019, will focus on Leonardo DiCaprio as fictional television actor Rick Dalton and his stunt double Cliff Booth portrayed by Brad Pitt. The pair will be struggling to adjust to a new Hollywood with DiCaprio's character being a neighbor of Tate's.