4. Rose Tyler: Let's be clear. Though Christopher Eccleston's Ninth Doctor is my favorite of all the 11, it was Billie Piper's Rose Tyler that really got the modern series going. It was her character that turned Nine from the scarred, probably PTSD-suffering loner into a man that could re-embrace his destiny as Earth's protector. As her relationship with the Tenth Doctor grew, we got to watch him fall in love not only with her, but all of humanity.

3. River Song: I was originally going to leave River out of this due to the fact her very existence makes canonicity scream like it stepped on a LEGO in the dark. In the end, I couldn't do it. Her appearances usually herald a headache, but she's also responsible for the single greatest line in the modern series.

Nazi: What do you think you're doing here?

River: Well, I was on my way to a gay, gypsy bah mitzvah for the disabled when I suddenly thought, "Gosh! The Third Reich's a bit rubbish. I think I'll kill the fuehrer."

2. Jackson Lake: It's been argued that the Tenth Doctor was actually Jackson Lake's companion, not the other way around. Lake believed himself to be the Doctor after a Cyberman infostamp backfired and imprinted him with the memories of the legendary Time Lord. What rose from the incident was a brave man that singlehandedly waged a war against the Cybermen until the real Doctor arrived. It's still my hope that somehow, when Smith finishes his run, he will regenerate into David Morrissey.

1. Donna Noble: When it came to a true partner, no one balanced the Doctor more perfectly than über-temp Donna Noble. Her all-too-brief one series was a welcome break from the constant romantic tensions that had dominated the last two series and would return somewhat in the fifth. She was the Tenth Doctor's best friend, most reliable helper and the one he clearly had the hardest time letting go of.