avclub.com released an article with Alan Tudyk in their Random Roles section, wherein they talk to actors about the characters who defined their careers.
Here's an excerpt in which Alan mentions Summer Glau is typecast.
AVC: All of your co-stars from that have gone on to have very different and interesting careers.
AT: Although, so far, I haven’t seen Summer Glau. I don’t know what Summer Glau wants or does. She might say, “I don’t want to do anything but science fiction.” But it’s what she does. That will be her thing, whether she wants it or not, I think. You can get what I have heard called—possibly by Joss Whedon—“the sci-fi ghetto.” You get actors who get in the sci-fi ghetto. Look at the people from Buffy. They get kind of trapped.
I don’t feel it, luckily. I’ve never felt trapped by it. And I think that times are changing. Look at Morena Baccarin, who is on Homeland. And science fiction is huge right now. Definitely in movies—it’s as much of a sure thing as you can have in movies. They tend to deliver, and definitely with Joss Whedon on board. I’ve been lucky enough to be able to still do things like 42 and things that aren’t Wash or Wash-like. I wasn’t pigeonholed.
I haven’t played a lot of Washs. I played Wash, and that was sort of the one, the one that’s the smartass kind-of-close-to-me guy. Whenever you’re introduced to the public first, you really either have to get away from it, or you embrace it and you fill that niche. I was playing extreme roles before I did Firefly. I did the gay German in 28 Days—I was the stoner in that, and a lower-class English in a movie about jousting. I was bouncing from a lot of different things. So the role of Wash, even though it is certainly the thing that I am approached about the most, it’s not the only thing that people see me as because they saw me doing something before.
Whereas Summer Glau, how old was she when she started Firefly? [She was 21. —ed.] So that was the thing that was so exciting—like wow, you do that. So she’s been embraced by the sci-fi community. And she’s in different sci-fi productions that see her talent but then also want to bring that into their production. There’s that. They’re like, we want a hit. Can we get that person from that? They have some sci-fi cred. There’s that as well. God bless it.
Read full article: Alan Tudyk on never playing the same role twice—except that one time