Tom Baker
The Tom Baker enhanced the alien nature of the Doctor, with the Doctor becoming more aloof, and with his strange, staring eyes, toothy smile, and incredibly long scarf, he often had the appearence of insanity in human terms. The fourth Doctor settled comfortably back into the "cosmic wanderer" role, cutting off his ties to UNIT and twentieth-century Earth early on in his seven seasons. Four of his companions (Romana (in two regenerations), Adric and Nyssa) were aliens, and another was a robot dog named K-9. He still remains the best known Doctor worldwide, and is generally considered the most popular of the Doctors so far.
Peter Davison
Peter Davison played a younger, milder, and sometimes much less confident Doctor. His casting was very much a reaction to Tom Baker's sometimes over-the-top performance; his characterisation was based somewhat on the first Doctor's portrayal, playing a less physical Doctor, with Hartnell's techiness tempered by Davison's own youth and mild manner. Other aspects of the show established links with the early years of the series: the Doctor again had three travelling companions, as in the first stories, two women and a young man. The stories also frequently had no pause between them, with the ending of one story leading into the next, something rarely seen since the early days of Doctor Who
Colin Baker
The sixth Doctor's character was, literally, violently opposite to the fifth Doctor's. In his first story, The Twin Dilemma, one of the first things the new Doctor did was attempt to strangle his companion Peri. His character was loud (as were his clothes) and frequently obnoxious, and is one of the least favourite portrayals amongst fans. The original plan was to have a gradual development of the new Doctor's character, however the BBC's dropping confidence in the show, and other factors prevented this from ever happening.
