10. Doctor Who
Because before she was Amy Pond... she was a Soothsayer! Karen stepped aboard the TARDIS as the Time Lord's coveted companion in Series 5's
The Eleventh Hour but that wasn't the first time she left her mark on the Whoniverse. Way back when (OK, it was only, like, 2008!), the up-and-coming actress appeared in Series 4's
The Fires of Pompeii which just so happened to also guest star the Twelfth Doctor himself, Peter Capaldi. So the Tenth Doctor and Donna Noble's venture to Volcano Day wasn't just a blast from the past, it was a glimpse into the future, too! That's
Doctor Who actors for you. You never know when/where they're gonna pop up next...