With the advent of the Doctor's 4th incarnation, his wanderlust returned and his connection with UNIT was a tenuous one at best. His personality, as before, changed quite drastically. He could be charming and good humoured but also brooding, unpredictable man .

While being interrogated by a Kaled (General Ravon) the Doctor deliberately disobeyed the command for silence in an attempt to make Ravon loose his temper and give away important information. This Doctor, then was confrontational and still possessed a rebellious streak, but with less bluster and more guile than before.

As he progressed through his incarnation, he displayed a tendency for slapstick and childish behaviour. However, there were times when the mask of joviality slipped and a more callous alien nature surfaced. To give one example the Doctor and his then companion (Sarah Jane Smith) discovered the body of a man they had met and befriended during one of their adventures. The Doctor looked dispassionately at the corpse and commented that his late brother must've called, and pushed the body aside. This led to Sarah Jane Smith (his companion) to almost accuse the Doctor of not being human. Yet it was not a lack of compassion but the ability to see the bigger picture without being distracted by smaller details that was one of the defining aspects of his 4th incarnation.

With the arrival of a companion of his own race, Romana, or to be more precise Romanadvoratrelundar, this was only the second Gallifreyan companion to travel with him. The Doctor resented her presence, especially as she proved to be academically and technically better qualified. Perhaps as result of this tension Romana embarked upon her first regeneration. This new Romana was more fun loving and less arrogant than her last incarnation and the relationship between the two thawed as a result. They worked well as a team with each respecting the other's skills and abilities. When Romana left, the Doctor became somewhat withdrawn. As the Doctor's fourth incarnation drew to a close, he seemed to lose much of his humour. In it's place a darker, moodier aspect took over.

After breaking free of a trap set by the Master, he witnessed a spectre from the future, his own future. It was as if death was waiting in the wings. Not long after, the Doctor was once more engaged in a battle with his nemesis. This time the battle ended in his downfall and, once again, he was forced to regenerate...