"Doctor Who," the longest running sci-fi show in history, has the first episode of Season 5 air at 9 p.m. EST tonight on BBC America.
The title character is played by Matt Smith, who took the reins from David Tennant at the end of last year's season. The change in actors has happened throughout the show's history, and Smith is the 11th person to carry the moniker of the Doctor.
How does it work? Simple - Smith plays an alien who, when his body is seriously hurt, can regenerate himself. It changes the exterior appearance of the the Doctor and plays havoc with his personality as well.
The Doctor travels about time and space in an old police box, which British officers used in the 1960s. It's a camouflaged spaceship called a TARDIS that's bigger on the inside than the outside - a state that's been referred to as dimensionally transcendental.
The Doctor uses his TARDIS to travel throughout time, often taking companions with him to help him in his wandering quest of righting wrongs and stopping evil monsters from destroying planets, which typically turns out to be Earth.