Star of Dexter , Michael C. Hall , was the narrator of a history channel documentary named Hitler’s War. He did it in 2005 and Dexter started in 2006.
I’ve been rewatching all of the David Suchet Poirot episodes, and there’s tons of actors in there from when they were quite young. Most I recognized right away, like Michael Fassbender, Damian Lewis, Joely Richardson, Emily Blunt doing a hilariously terrible American accent, and Christopher Eccleston.
But there was one episode where I just could not place the actor, so afterwards read the credits to see who it was. It was Peter Capaldi. Even more irritating was that I had just seen the Christopher Eccleston episode.
Fred Stoller made a career out of being a character actor
When you see him you will probably recognize him.
He was also a Seinfeld staff writer for one season and was credited for two shows.
http://www.imdb.com/name/nm0831550/?ref_=nv_sr_1
He wrote a book “Maybe We’ll Have You Back: The Life of a Perennial TV Guest Star” that I liked. Amazon also has"My Seinfeld Year" available as a Kindle single.
The animated series Robot Chicken once did a rather vicious parody of A Shot at Love with Tila Tequila. When the credits rolled, it seems that Tila Tequila did the voice for it.
I was watching an ep of “Soap” on one of the oldies channels. There’s a quick scene with a hot chick playing a hooker. When the credits ran, I was really surprised to see that the hot chick hooker was played by. . . “Soap” producer Susan Harris.
He deliberately kept his name out of the credits so people wouldn’t think the film was a comedy, but I was surprised to learn of Mel Brooks’ extensive involvement (as an executive producer) in The Elephant Man.
He’d already been starring in Six Feet Under for four years by that point. I understand narration work is a solid earner as a sideline for a lot of “name” actors - it always amazes me who crops up in these documentaries.
Nancy Walker, Rhoda’s mom and the Bounty quicker picker upper spokes person wrote, “Can’t Stop The Music”, the Village People’s movie.
The DC Animated movie Batman vs Robin has Al Yankovic (yes, the “Weird” one) as the voice of the Dollmaker (a dark villain even by Batman standards).
I watch a lot of crime documentaries. One that aired on the ID channel recently was called “Betrayed.” One of the producers: Kevin Spacey.
Similarly, I watched the BBC Miniseries (shown here on PBS) I, Claudius when it first aired in 1976. Years later, in the 1990’s I watched it when PBS ran it again. Now, I knew that John Hurt played Caligula and that even “Sallah”, John Rhys-Davies had a small part as Macro, but was surprised to see that Patrick Stewart played Sejanus! Sure, I didn’t know who Patrick Stewart was in 1976, but even if I did, I wouldn’t have recognized him with his full head of hair 
Robby Benson was something of a punchline in the 1970s for starring in sappy treacle such as Ode to Billy Joe, One on One, and Ice Castles.
To this day, whenever I see his name pop up on one of the 6 Friends episodes he directed, I chuckle a little inside. (To be fair, he’s a pretty accomplished TV director; I just have trouble separating the name from his earlier schmaltzy acting work.)
When I saw Richard Harris in the first Harry Potter movie, I thought “Huh: dude has the same name as the guy who sung that stupid song ‘MacArthur Park.’ Oh well, it’s a pretty common name.”
I guess that song did sorta redeem itself when it supplied the background for a great line in Priscilla, Queen of the Desert.
The actress who played Sgt Dori Doreau in the TV series Sledge Hammer, Anne-Marie Martin, wrote the movie Twister.
That’s probably because she was married to the writer Michael Crichton. But still.
I think anyone alive in England during the 70s that ever carried a spear in a Shakespeare play was in I, Claudius.
Anyone besides me think he’s actually better-looking without hair?
Ain’t that the truth! 
Hell, even Ian Ogilvy who starred as Simon Templar in that lousy remake of The Saint was in it.
Do an image search for “Patrick Stewart Midsummer Night’s Dream” and get back to us.
Although Al Yankovich is fairly well known for doing cartoon voice cameos I was surprised to see him doing the voice of the main character in Milo Murphy’s Law.
The first time I saw Tony Dow’s name as a producer was on Babylon 5. Kind of funny if you think about it.
Charles Nelson Reilly and Jackie Mason doing voices on Spongebob Squarepants.
Adam West and Burt Ward as the young Mermaid man and Barnacle Boy on Spongebob Squarepants.
I had never even heard of Micheal Crichton before Jurrasic Park so I was surprised to find out he wrote the book Adromedia Strain is based on.
MrAtoz writes:
> Peter Weller, surprisingly enough, has a Ph.D. in Art History from UCLA, focusing on
> the Italian Renaissance. He’s also taught history courses at Syracuse. Imagine taking
> a history class and having Robocop as your professor!
And if that would be weird, how about the fact that while she was working on her Ph.D. and just after getting it, Mayim Bialik taught a few classes about neuroscience to her home school community at the junior high and high school level? (I’m not sure what a home school community is, but I’ll pass on that for the moment.) This was just before getting cast as Amy Farrah Fowler. Probably the students in those few classes knew that she’d been an actress, but she’d been out of it for a while. Imagine watching The Big Band Theory for the first time and noticing that the woman playing a neuroscientist was the one who had taught you something about the field several years before: