The fifth incarnation of the Doctor was perhaps the most vulnerable of them all. Unlike his previous incarnations, he was given no chance to rest. Within minutes of his regeneration he half ran and was half dragged towards his Tardis. This proved to be too much for him and he collapsed to the ground. Despite his youthful exterior, he was somewhat weaker this time.

The fifth Doctor seemed dogged by misfortune from the start. With his regeneration failing he became more and more disorientated, mentally slipping back to former incarnations before finally finding respite in the zero room. Even then, his time of rest was short lived as the Tardis was plunged back to event one, the birth of the universe. He escaped only to find himself in mortal peril as yet another trap is laid for him on the planet Castrovalva. It seemed then, that the odds of survival were stacked against him. He persevered and this new incarnation finally began to establish itself.

He possessed a youthful vigour and enthusiasm that had waned with his last incarnation. He had a passion for cricket and proved to be and excellent sportsma. He was energetic, dashing from one location to another with his companions trailing behind him. This Doctor had a rather acidic humour, with Tegan often being on the receiving end of his sharp tongue. When asking if the Doctor was not returning back to Gallifrey, he swiftly replied, "You know Tegan, sometimes you take my breath away!"

Death seemed to plague the Doctor. His attempts to mediate between the Silurians, the Sea Devils and Humans failed, with the 3 races wiping each other out. It seemed that the Doctor was able to handle successfully events on a large scale such as defeating the Daleks and Cybermen but it was the smaller things, such as his relationship with his companions where he was more of a failure. Despite defeating the Cybermen's goal of genocide, he was unable to prevent the death of his companion Adric who was tragically killed on board an exploding freighter. His relationship with Tegan was an especially close one. Even so his battle with the Daleks led to her departure who told him she was sick of all the death and violence and that she couldn't go on. This proved to be something of a shock to him as he had failed to notice how she had suffered. For the first time he admitted that he should perhaps mend his ways. Perhaps his single minded attitude led to the end of his friendship with her? when he entered a network of caves, with his new companion, Peri, she fell into a sticky substance that stung her legs. He brushed it off her with his hands "dismissing it as probably quite harmless"t. The substance was called spextrox which led to a fatal conditon called spectrox toxæmia. Despite his shortcomings the Doctor in an act of bravery and determination overcame the disease and many other obstacles to gather an antidote. Unfortunately the Doctor dropped some of the antidote while trying to unlock the Tardis doors. There was only enough for one of them so gave it to Peri thus sacrificing himself to save her.