3. Queen Elizabeth I
Queen Elizabeth has been threatening to play a big part in the show for a long time now. It was in the second episode of series 3 that she first showed her face, she was later mentioned in The End of Time (Specials 3), The Beast Below (Series 5, Episode 2) and later 'The Wedding of River Song'. The implication is that after a brief and passionate love affair (more than there phone numbers was shared if you know what I mean...) the two decided to elope together however the Doctor left her standing in a glade waiting for her husband-to-be to sweep her off her feet and into happy marriage. It explains why she wants him dead by the time she meets him at the end of 'The Shakespeare Code' (Series 3, Episode 2). Due in part to certain shots of Elizabeth running through forests I think that she will be the Tenth Doctor's sort-of-companion as opposed to Rose. The two, I assume spent a lot of time together and we are probably going to see a lot of that, in the 50th anniversary special, taking us all the way to the moment where Elizabeth is spurned in the woods. I think she's going to play a large part in the episode unlike the Daleks and the Zygons who are actually the next entry on this list.