“Mercy Graves is the ruthless, cunning, right hand and bodyguard to the notorious Lex Luthor – serving 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.”
It seems like the character is being brought in as part of the Superboy plot thread that will seem to play a role in the second season.
Gumede is best known for starring as Ashley in the Doctor Who Christmas Special that aired Christmas Day 2014 to an audience of 9.6 million viewers.
Within the pages of DC Comics, the Graves character was introduced in a 1999 issue of Detective Comics but comics were her second medium. That’s because Graves, a sardonic martial-arts specialist in a mini-skirt and chauffeur’s cap, first appeared in 1996 in Season 1 episode of Superman:The Animated Series.