The character Klaus Mikaelson was originally meant to be killed off in The Vampire Diaries. Diarios de vampiros (2009), but the character's ever increasing popularity granted him survival and a spin-off show.
Joseph Morgan is married to Persia White, who played Bonnie's mother in The Vampire Diaries. Diarios de vampiros (2009).
Nathaniel Buzolic, the actor portraying the role of Kol Mikealson, auditioned and was almost cast as Stefan Salvatore in The Vampire Diaries. Diarios de vampiros (2009).
Nathan Parsons, who plays the werewolf Jackson, left the show during season one to play a vampire on HBO's True Blood (2008).
Only one of the Mikaelson children is American: Riley Voelkel. Joseph Morgan is English, Claire Holt and Nathaniel Buzolic are Australian, Daniel Gillies is from Canada, and Casper Zafer is a Ukrainian-British actor. Devon Allowitz is also an American, but he's excluded since his character Henrik has only appeared in archive footage in the series.