Doctor Who, the classic long-running twice-revived British sci-fi TV series, is an ingenious example of a franchise-friendly story: Its main character, The Doctor, is an alien who necessarily changes his appearance and personality every time he faces a serious injury. No more pretending that two totally different-looking actors are portraying the same character or embarrassing gaps between two different portrayals—that’s the way it’s supposed to be! It doesn’t mean there aren’t favorites, though. Tom Baker, the Fourth Doctor, is the early, “classic-Doctor” favorite (and the best-known in the U.S.), but David Tennant’s witty, chatty Tenth Doctor, who just finished up his run in January, set a new standard in the portrayal of time-traveling aliens. How will Matt Smith compare with Tennant, and all the previous Doctors?