Over the years, Doctor Who has given fans different accounts of what really happened when the titular character stole a TARDIS and ran from his home planet of Gallifrey, though the numerous showrunners of the sci-fi series have deliberately refused to offer a definitive answer to this question.
And it’s a fairly important question, too. After all, this was the incident that kickstarted the Doctor’s journey across time and space. It was Steven Moffat, the former showrunner, who last tackled this question during Peter Capaldi’s second run as the 12th Doctor. As it came to pass in season 9’s “Hell Bent,” we learned that the Last of the Time Lords were scared about the legend of the hybrid, a prophecy that foretold the destruction of Gallifrey at the hands of a ruthless warrior. The Doctor believed that he was the hybrid. Though he also later acknowledged the immortal Ashildr to be a point of interest in the prophecy.
Going further back, Russell T. Davies gave us a different answer in “The Sound of Drums.” As the 10th explained, Gallifreyans who got into the Academy would be taken to the Untempered Schism, a gap between the fabric of reality “through which could be seen the whole of the vortex.” The Doctor attributed this experience as a child to the Master’s madness.
“You stand there, eight years old, staring at the raw power of time and space, just a child. Some would be inspired, some would run away, and some would go mad,” he noted. When Martha asked what he had done, the Doctor admitted that he decided to run away. But what did he see in the vortex that made him so scared?
While we may never know the answer for sure, Doctor Who canon has revealed that he also stole the Hand of Omega from Gallifrey’s vaults before departing, a powerful weapon with galaxy-altering capabilities. In “Remembrance of the Daleks,” the Doctor takes the weapon to Earth in 1963, using it as bait to lure the Daleks in. Though at that stage in his life, the time traveler hadn’t encountered Davos’ minions yet.
But what if the Doctor saw the Time War and the end of the universe in the Untempered Schism as a child? Perhaps that’s why he ran away, with one of the most dangerous weapons in existence no less. The Last of the Time Lords knew that a war was imminent, only then, he didn’t know that their enemies would be the Daleks.
Alas, by the time he tricked the Daleks with the Hand of Omega to destroy their own homeworld of Skaro, they’d grown too powerful. This makes the Doctor’s destiny even more tragic. The reason he ran away was to prevent the death of his species, and little did he know that he’d actually play a part in their destruction later on. Although, Moffat retconned this in “The Day of the Doctor,” instead revealing that different incarnations of the titular hero came together to find an alternative to committing genocide.
Then again, we’d be naive to simply take the 10th Doctor’s word for it. As River Song would say, the first rule of traveling with the Doctor is that “the Doctor lies!”