Doctor Who has the power to turn an unknown actor into an overnight household name. Just take Matt Smith, for example. He was relatively unknown before he was cast as the titular Time Lord but as soon as was announced he became the hot topic of conversation when his face was slapped on the front cover of every newspaper and magazine across the land. Granted they were all saying he was too young to play the part, but there's no such thing as bad press. Apparently. Given the amount of scrutiny that Doctor Who is under, it's inevitable that its actors - whether it's in a leading or guest role - find themselves being placed on a pedestal. When they eventually leave the series they no doubt feel the pressure to go on to bigger and better things which usually involves moving across the pond and trying their luck in America. As this lis t will prove, though, not all of them have managed to leave their mark in the US. Doctor Who as a series is constantly gaining a larger viewership in America but even that hasn't helped some of the show's alumni make the leap from the UK to the US. One of the biggest success stories of most recent years is Karen Gillan who has seemed to make the transition effortlessly. Just two years after leaving her role as Amy Pond she had landed her very own ABC sitcom (admittedly it got cancelled but the point still stands) but some of her co-stars are still to maintain their grip on the steep slope of the competitive Hollywood hills. Here are 5 of them.