I don't know much about Doctor What, so I'm not going to pretend like I do. I do know that the latest girlfriend on the show is called Amy Pond, played by Karen Gillan, who gave birth to the Doctor's child, a young man named Rory Williams. Rory is also the man who repairs the Doctor's DeLorean car, with which he travels through time to protect the Rebellion from the forces of the Borg. He also has to make a lot of phone calls in an old phone booth.
I think I got most of that right.
Anyway, Steven Moffat, when he's not racking his brain trying to figure out how he's going to explain the conclusion to the third season of Sherlock when that show finally comes back, has confirmed the speculation that Gillan will be leaving the show in the middle of the next season, but he's also announced that her replacement has already been cast, in the form of 25-year-old Jenna-Louise Coleman:
It always seems impossible when you start casting these parts, but when we saw Matt and Jenna together, we knew we had our girl. She's funny and clever and exactly mad enough to step on board the Tardis. It's not often the Doctor meets someone who can talk even faster than he does, but it's about to happen. Jenna is going to lead him his merriest dance yet. And that's all you're getting for now. Who she's playing, how the Doctor meets her, and even where he finds her, are all part of one of the biggest mysteries the Time Lord ever encounters. Even by the Doctor's standards, this isn't your usual boy meets girl.
I can't say that I've ever heard the name before, but Coleman has apparently had a bit role in the Captain America film, as well as a few BBC television credits, to which she'll be able to add Professor Who some time next year.