maestro, Russel T Davies likes to do that. He also likes to use character's names again. Gareth David Lloyd, who plays Ianto Jones, played a different character on a totally different show by Russel T Davies called Ianto Jones (the character not the show).
So far, the only actor who was on Dr Who and played a different character is Naoko Mori. She was in an episode in the first season called Aliens In London. Okay, I know, I sound like a total geek. I just happened to have seen that episode a few weeks ago. CBC has a new channel and they started Doctor Who from the beginning of the new series. Really, I'm not a geek. Just a little obsessed with Torchwood. Just a little.
Not so, my fine geek! The actress who played Gwen was in the first season for Who, in the Dickens episode. She played the psychic who was killed by the alien/ghosts, the servant of the man who owned the mortuary. Also, just stretching a geek point, (and a LITTLE bit of a spoiler but not much), Martha Jones also appears in Torchwood, and she first appeared as a different character in Who.
Captain Jack was in Doctor Who, the last five episodes of the first season and the last three episodes of the third season. He will also be in the fourth season.
My geekdom will now end.
Your geekdom will never end!
Jeff, the cats do look alike. Ty is a cutie. (ps, there are several typos on the website. pm me and I'll tell you)
(there is no forehead slap smiley. Someone get on that, will ya)