4. April O'Neil (Teenage Mutant Ninja Turtles)
Headstrong and passionate, April is a roving television news reporter with a head for adventure. She isn't afraid to put herself in harm's way to get a scoop and has found herself in some very dangerous situations as a result, making her an experienced and seasoned adventurer. As a companion to the Doctor, she would be brave, resourceful and enthusiastic. I think she would relish the opportunity to jump in the TARDIS with him and see the universe. The two might disagree occasionally due to April's stubbornness, but she would undoubtedly offer him a heroic and quick-thinking sidekick who could prove incredibly useful on his adventures.