William Hartnell played the first Doctor. Then:
Tom Baker--The man who first defined what it meant to be "The Doctor". All the ones to come after him were influenced by him.
Peter Davidson--Another of my five favorites out of the eleven that there are. My favorites go:
1. David Tennant #10
2. Tom Baker #4
3. Christopher Eccleston #9
4. Peter Davidson #6
5. Matt Smith #11
I find it funny that the eleventh Doctor is played by a man named Smith. The Doctor uses the name John Smith quite often when he has to give a name.
Colin Baker--I didn't want to put him in here, but I suppose that the list wouldn't be complete without him. I don't like him at all. I felt like he was trying too hard to be like Tom Baker while still being his own Doctor. It didn't work. Plus, his Doctor was a bit of a jerk.
Paul McGann--ended the original series in 1996
It was then begun again in 2005 with:
The Doctor. David Tennant. The amazing, geeky, wonderful, not ginger, rude, no second chances, lucky Doctor. :) My absolute favorite Doctor. There wasn't one as good as him before, and there won't be again. He was the Doctor. You can't be more Doctor than he was.
Then, the Doctor regenerated yet again
And is now:
The Doctor travels in a ship called the TARDIS (Time and relative space dimensions in space capsule) It looks like a police box and "blends in". No one really pays attention to it in other words. It was programmed that way. So it's almost invisible to other people. It's bigger on the inside. Much bigger. Doctor 11 says that he fell all the way to the library and into the pool.
The Doctor always travels with a companion, up to three at a time.
The main ones in the newer seasons are:
Rose Tyler--She meets the Doctor while being attacked by a roomful of plastic mannequins in the basement of the shop she works at. She stays with him for two season. Christopher Eccleston-David Tennant. She and the Doctor fall in love, but she is forced to leave him at the end of season two when she is stuck in an alternate universe while fighting the cybermen. She finally gets back to him in episodes 12 and 13 of season four, but has to return to the alternate universe a second time. This time she has her own Doctor though. AND he's human! :) If you watch, during the time after she was separated from the Doctor and before she gets back to him, you can see her in various episodes. One example being the episode 10 season 4 "Midnight". You can see her on one of the television screens calling to the Doctor.
Mickey Smith--Rose's ex-boyfriend, still friend. He comes along with the Doctor and even helps save planet earth a couple of times.
Captain Jack Harkness--You meet him in season 1 episode 9 "The Empty Child" and he shows up in several other episodes afterwards. He is killed in season 1 episode 13 "The Parting Of Ways" by the Daleks, but Rose brings him back to life after she looked into the heart of the tardis and saw all of time and space. But, she brings him back too much and now he will live forever. He can never die, but he does keep getting older. He is probably the Face of Bo in later episodes. If so he finally does die for the last time in Season 3 Episode 3 "Gridlock" saving everyone on the planet. His dying words were "But know this Timelord, you are not alone." *gasp*
Martha Jones--She meets the Doctor when the hospital that she is training in gets beamed to the moon. The Doctor had been admitted to the hospital under the name John Smith because he felt something was up there. She leaves the Doctor by her own choice at the end of the season, 3, after they have defeated The Master, the only other timelord in existence. She is in love with him, but he is still missing Rose.
Donna Noble--meets the Doctor for the first time in the special "The Runaway Bride" after losing Rose. She doesn't want to go with him, but regrets it afterwards and spends a long time searching for him, until they meet again season 4 episode 1 "Partners in Crime". She wants to stay with him forever, but in the end of the season she becomes part Timelord and her human brain can't handle everything inside it. The Doctor is forced to erase her memory of him, and she can never see him again because if she did, she would remember, her brain would overload and she would die. She ends up getting married and the Doctor gives her a lottery ticket. ;)
Amy Pond--The new Doctor, number 11, crash landed in her backyard when she was only seven and fixes a crack in her wall that leads to a prison. He promises her he will be back in five minutes, but he miscalculates and doesn't get back until she is 19. He defeats Prisoner Zero, who escaped through the crack in her wall all those years before and has been living in the house just in the corner of her eye. He then leaves again just to take the Tardis for a test run. He doesn't get back for another two years when she is 21 and takes her with him the night before her wedding.
It's late, so I guess that's it for now. I might follow up with another post some other time. But I highly recommend the show. It is wonderful.