A TV spinoff is a way to give a popular minor character more of the spotlight, or, more realistically, is a way for executives to fill a gap in their schedule without thinking of a new idea.
Spinoffs like Frasier, Joey, and Angel have all taken characters out of their natural settings and thrust them into brand-new ones, but that's not what we're interested in with this list.
Instead, we want to focus on characters from one TV show who appeared in a completely different TV show, while still being portrayed by the same actor. We're not counting spinoffs, but will allow a little leeway for shows that may be set in the same universe, but don't cross over all that much.
While most of the actors on this list made one-off appearances outside their main show, a few actually went on to become regular fixtures on other programmes. For many, the jump to a new show was just a brief cameo that didn't amount to much, but, in a couple of cases, the move actually made the characters more famous.
Try and wrap your head around this one, because some of these entries are about to get seriously meta.
10. Kiefer Sutherland - Jack Bauer (24 & The Simpsons)
The Simpsons' 2007 episode 24 Minutes is one big Treehouse of Horror-type segment spoofing Fox's action-drama, 24.
That show stars Kiefer Sutherland as Jack Bauer, a counter-terrorist agent who usually ends up having to stop someone important from being shot or blown up.
The action takes place in real-time over 24 hours, although the show had commercials so it's not entirely clear how that works!
24 Minutes took this idea and applied it to Springfield Elementary. Lisa leads the Counter Truancy Agency (CTU) as they try and stop a stink bomb from being detonated at the school's bake sale. The episode is really fun, a neat little twist on the regular format of the show, and it also features some very appropriate guest stars.
One of those is Jack Bauer, who makes an appearance to arrest Bart after he made a prank phone call to him. Sutherland reprises his role as Bauer and is joined by Mary Lynn Rajskub, who is also in character as 24's Chloe O'Brian.
These 24 cameos are the icing on the cake for the episode, even if Bauer's obsession with Bart does lead to a nuclear bomb going off. Don't worry though - it was in Shelbyville.