It sounds like DC Universe's Titans will eventually introduce Lex Luthor, because his right-hand woman is coming to season 2.
According to Deadline, Natalie Gumede has been cast in the recurring guest role of Mercy Graves. This take on the formidable bodyguard of Superman's nemesis is described as "ruthless and cunning," Mercy serves her boss with "unquestioned loyalty. Her connection to the Luthors runs deep, as Mercy has been a friend of the family and in Lex’s life since they were young.”
Like Harley Quinn before her, Graves debuted in animated form before finding her way to the comics. Since then, other live-action incarnations/variations of the character have appeared in Smallville, Supergirl and Batman V Superman: Dawn of Justice.
Gumede is arguably best known for playing Ashley Doctor Who, but has also appeared in the likes of Jekyll & Hyde, Death in Paradise, and Clubbed.
Titans season 2 does not have a premiere date yet.