The Fourth Doctor's regeneration into the Fifth was a problematic one, and nearly failed, with the Doctor briefly taking on personality aspects from his four previous incarnations. After recovering in the fictional city Castrovalva, he continued his travels with Tegan Jovanka, Nyssa and Adric.before
After trips to the future and the past encountering villains such as Monarch and the Mara, the Fifth Doctor was confronted with tragedy when Adric died trying to stop a space freighter from crashing into prehistoric Earth.
When the Doctor met a new companion, an alien boy stranded on Earth by the name of Vislor Turlough, he did not know that Turlough had been commissioned by the Black Guardian to kill him. Soon after, Nyssa left to help cure Lazar's Disease on the space station Terminus. After meeting the entities known as Eternals racing in yacht-like spacecraft for the prize of "Enlightenment", Turlough broke free from the Black Guardian's influence, and continued to travel with the Doctor and Tegan. The Doctor met three of his previous incarnations when they were summoned to the Death Zone on Gallifrey by President Borusa, who was attempting to gain Rassilon's secret of immortality.
After further adventures in which the Doctor re-encountered old foes including the Silurians and the Sea Devils both Tegan and Turlough left the TARDIS. Tegan would find the death and violence they encountered on their travels too much to bear, and Turlough returned to his home planet of Trion in the company of his younger brother, as well as other exiles of Trion, from the planet Sarn.
Ultimately, the Fifth Doctor and his last companion Peri Brown were exposed to the drug spectrox in its deadly toxic raw form on Androzani Minor. With only one dose of the antidote available, he nobly sacrificed his own existence to save Peri, regenerating into the Sixth Doctor, expressing doubt for the first time that regeneration might be possible. but now he is played by Matt Smith and wife Daisy
Revived Series AppearancesEdit
Somewhere in his life (perhaps set after the events of Snakedance) he crashed his TARDIS into the TARDIS of the Tenth Doctor and consequently nearly opened a "Belgium sized" black hole because of the paradox caused, which the Tenth Doctor also uses to explain the notably aged appearance of his former self. However the Tenth Doctor, remembering the event, knew how to stop it because he recalled watching himself correct the mistake when he was the Fifth Doctor.