Filled with wanderlust and a renewed curiosity towards exploring time and space, the Fourth Doctor left all ties of his previous incarnation's exile behind on Earth, setting off to travel the Cosmos. He initially travelled with Sarah Jane Smith and Harry Sullivan, but Harry chose to remain on Earth when the opportunity arose. The Doctor and Sarah continued on their adventures until the Doctor was summoned to Gallifrey, necessitating that he leave Sarah Jane behind as humans were not allowed on Gallifrey.
After tangling with the Master on Gallifrey, he met and travelled with Leela of the Sevateem. During his travels with Leela, the Doctor gained a new companion in the robot dog, K9. Returning once more to Gallifrey to stop an invasion of Vardans, Leela and the original K9 stayed behind there.
On the White Guardian's orders, the Doctor began looking for the Key to Time with fellow Time Lady Romana and K9 Mark II. Once that search was concluded, the Doctor and Romana went on the run from the Black Guardian. Not long after, Romana regenerated into a new body and continued to travel with the Doctor and K9. When they attempted to answer a Gallifreyan summons, the trio accidentally passed into the smaller universe of E-Space.
During his travels in E-Space, the Doctor gained a new companion in the teenaged mathematical genius Adric. Romana and K9 stayed behind in E-Space as the Doctor and Adric departed for N-Space. There, they encountered a Trakenite princess named Nyssa and a human named Tegan. The foursome successfully prevented the destruction of the universe by the Master, but only at the cost of this incarnation's life after he fell to his death. The Watcher would then essentially fuse with The Doctor to help him move on into his next incarnation.
Doctor Who Rebirth AdventuresEdit
The Fourth Doctor along with his previous, and future incarnations was one of the versions of The Doctor captured by the Timelords and imprisoned on Gallifrey, with all of them in a single cell in the hopes that the paradoxes would destroy all of The Doctor's lives. (The Time Well: Part Two)