In a video message to the fans in attendance during the iZombie panel at San Diego Comic-Con 2017, actor Robert Knepper announced that he was promoted to series regular for creator Rob Thomas's iZombie Season 4. Knepper plays Angus DeBeers, the father of Blaine DeBeers (David Anders), who has been somewhat of a series antagonist.
The last season ended with Blaine killing his father, but in a show about zombies, you know that won't keep a good character down. Knepper tells Anders that all is forgiven — that might be the case between the two actors, but I'm sure Angus is going to have some issues with his progeny, once saying that he was "a waste of sperm."
Knepper has been very busy of late, playing recurring characters last year on iZombie, Homeland, and Prison Break: Resurrection. His name has also come up recently in speculation that Richard Dragon would be the new big bad for Arrow Season 6. That hasn't been confirmed, but if the casting rumor is true, that would mean Dragon (and potentially his Longbow Hunters) would menace Star City. One of this allies is William Tockman/Clock King, a role that Knepper has played on both Arrow and the Flash. Being a series regular would make playing a recurring role on another series difficult, but since it's a mid-season series on the same network and from the same studio, it's not impossible.
Here is the video Knepper recorded for Comic-Con: