A Biography of the Doctor
The Fourth Doctor
"I'm a Time Lord."
"I know you're a Time Lord."
"You don't understand the implications. I'm not a human being. I walk in eternity."
- The Fourth Doctor and Sarah Jane Smith in Pyramids of Mars
The Fourth Doctor was very much the bohemian eccentric. Unlike his third incarnation, he wasn't content to stay on Earth working for UNIT, but spent all of his time exploring the universe. He had a very casual manner and mannerisms. He routinely greeted people with his broad, toothy, grin and treated them as if they were already friends. The best example of this is his habit of offering people jelly babies.
Part of this persona was an air of naive innocence, although this was at least partly an act. The Fourth Doctor was very contemplative, thinking in a way that looked like alien detachment from a human perspective. He would use ploys such as the jelly babies and playing with his yo-yo to distract opponents and make them underestimate him. When he began travelling with the Time Lady Romanadvoratrelundar he began using far more tomfoolery, flippant retorts, and wisecracks - something which infected Romana when she regenerated.
This Doctor is very much opposed to violence, except in exceptional circumstances. He was extremely uncomfortable when travelling with Leela, who always carried potentially deadly Janis Thorns. However, as time went on, he was more willing to use force to resolve threatening situations.
Towards the end of his life the fourth Doctor became far more irascible, moody, and even brooding. Presumably the appearance of his watcher made him contemplate his own death. This was not an entirely new side to the fourth Doctor, as he had displayed moments of this throughout his life. However, this did not dilute his sense of duty to act in the best interests of his friends and the entire universe.
The fourth Doctor's appearance is best summed up by the word bohemian. He wore a floppy hat, a baggy coat, and - most notably - a ridiculously long scarf. His toothy grin and brown curly hair were also particular features. He frequently towered over others, due to his height.