10. Steven Moffat
A writer on the show since its return in 2005, Steven Moffat wrote many of the most popular episodes of the time including The Doctor Dances, The Girl in the Fireplace and the scary-ass demon garden statues episode that some considered one of the best, Blink -- all of which won Hugo awards. In 2010 he took over as showrunner -- meaning he writes many episodes, edits all episodes, and decides the show's general direction -- with the arrival of Matt Smith's Eleventh Doctor.
Reception of the series has been mixed since Moffat took over. Moffat's fondness for clever stories worked great when he wrote an episode or two a season, but attempting to stretch the same ideas over an entire season has created stories that are less coherent... and with some alarmingly sexist overtones. However, the ratings are doing well -- and are on the rise in America -- so Moffat is expected to continue in the role through season 8 and 9, at least.
11. Sonic Screwdriver
The Doctor hates weapons almost as much as he hates soldiers. He doesn't carry any weapons of his own (with the rare exception), but instead defeats armies and stares down intergalactic evil with his wits, his fast talking and his handy sonic screwdriver.
It's basically used as a magic wand for all things technological. It can scan items to give him information (think Star Trek's tricorders). It can also open locked doors, disable electronics (including weapons) and control computers. And every time the Doctor regenerates, his sonic screwdriver tends to get a new design as well.
12. Renegade Time Lords: The Master and The Rani
The Doctor's arch-nemesis, The Master (most recently played by John Simm), is a renegade Time Lord that also survived the Time War. His goal is to rule the universe and hurt the Doctor as much as possible, the latter of which he manages to do every few years. The Master is supposedly dead... but that rarely seems to stick, so we may yet see him show up again.
The Rani is another renegade Time Lord -- or, technically, Time Lady -- who has served as the Doctor's nemesis over the years. She's usually less interested in world domination and more interested in science... though she rarely cares who or what she might hurt in the name of scientific progress. She's not yet been seen in the new series, but rumors suggest she could show up this season.
13. The Christmas Special
Being considered a children's show in Britain (with an enormous adult following), an extended-length special is made for the holidays. These stories are usually one-offs that may not tie into the rest of the season at all -- but what they all have in common, of course, is a focus on Christmas.
The end result is usually fun, even if it's not always very weighty, featuring a lot of running in the snow and the Doctor occasionally falling down chimneys (Christmas Eve on a rooftop. Saw a chimney, my whole brain just went 'What the hell!). In the last Christmas special, however, was a big one, plot-wise, with the Doctor regenerating.
Now you're more or less up to speed on all things Doctor Who... so you can head over to Netflix or Hulu to watch your way through the revived series or catch the latest episodes Saturday nights on BBC America. Geronimo!