4. Rachel Hurd-Wood
Rachel Hurd-Wood made her acting debut in what many might consider the precursor to Doctor Who. Peter Pan, the story of a young girl desperate for an adventure who runs away with a guy much older than he looks. She played Wendy, and even when she was thirteen she was already nailing the role of the companion. She has continued to work steadily into adulthood, appearing in an adaptation of the Oscar Wilde novel The Picture of Dorian Gray, and is due to star in two more international productions that will come out within the next year or so. But at the same time, she is very much an unknown actress for most casual audiences that will feel like a blank slate, without too many preconceived ideas of what she would be like. Most appealing for us is the fact that she has very classic features, and seems like she would be the perfect type to play a historic companion. Sure, we have the Paternoster Gang in Victorian England, but they're getting close to that point where they'll feel like they've overstayed their welcome if they show up too frequently. And there's something to be said about having someone from the past travelling with the Doctor in the TARDIS, getting to see things that they never even dreamed of an having to assimilate to even the technology that we take for granted.