The Hybrid

File:The Hybrid Confession - Heaven Sent - Doctor Who - BBC

The Twelfth Doctor confesses about his knowledge of the Hybrid. (TV: Heaven Sent)

The Hybrid was a Gallifreyan legend that said all Matrix prophecies predicted that a hybrid creature, thought to be crossbred from two warrior races, would stand over the ruins of Gallifrey and unravel the Web of Time, breaking a billion billion hearts to heal its own. Rassilon searched for information about the Hybrid. (TV: Hell Bent)

References

The Daleks receive the Doctor's regeneration energy from Colony Sarff on Skaro. (TV: The Witch's Familiar)

It was popularly supposed that the two warrior races would be the Time Lords and the Daleks. (TV: Hell Bent) Davros attempted to fulfill the prophecy by giving some of his Daleks regeneration energy taken from the Twelfth Doctor, transforming them into Time Lord hybrids. (TV: The Witch's Familiar) However, the Doctor later revealed the Daleks would never allow anything to be half-Dalek. (TV: Heaven Sent)

The Twelfth Doctor claimed at various points to possess special knowledge about the Hybrid, going so far as to one point stating that the Hybrid was "me". (TV: Heaven Sent, Hell Bent) It was suggested that knowledge of the Hybrid prophecies from the Cloisters originally drove the Doctor from Gallifrey, and Ashildr proposed that the Doctor himself was a half-human half-Time-Lord hybrid. (TV: Hell Bent) However, the author of the Time Lord Academy textbook on Gallifreyan history believed that the Doctor was bluffing when he said he was the Hybrid. (PROSE: A Brief History of Time Lords)

Other possible candidates for the hybrid included the part-human part-Mire Ashildr, (TV: The Girl Who Died) the simultaneously-human-and-Zygon Osgood, (TV: The Zygon Invasion) the "part-human part-wolf" Rose Tyler, the post-metacrisis Doctor Donna, and the half-Time-Lord River Song. However, none of these quite fit the prophecy. (PROSE: A Brief History of Time Lords)

In the Cloisters at the end of the universe, Ashildr posited to the Twelfth Doctor that the Hybrid could be interpreted as referring to more than one being: specifically, the pair of the Doctor and his companion Clara Oswald. Just prior to losing his memories of Clara, the Doctor indicated that his reckless actions in trying to prevent her death made him the Hybrid. (TV: Hell Bent)

In 2002, Sam Jones told Griffin about a Gallifreyan prophecy concerning a hybrid. She said the Doctor was a hybrid, his father a Time Lord and his mother a human, and that he was destined to unite the two races and "bring good old human niceness into their alien society". Though she thought she was bluffing to stall Griffin, the Eighth Doctor later asked her who had told her about the prophecy. (PROSE: Unnatural History)

Behind the scenes

• Although Hell Bent, among other series 9 episodes, offered multiple possibilities as to the identity/nature of the Hybrid, showrunner Steven Moffat, in an interview for Doctor Who Magazine #504, confirmed that he intended that the Hybrid was the pairing of the Doctor and Clara. He retroactively linked this fact to the reason why the Doctor's TARDIS exhibited some hostility towards Clara in series 7.
• In series 12, opening two-parter Spyfall had the Spy Master reveal that he had destroyed Gallifrey and left it in ruins. In the second part of the two-part finale, The Timeless Children, has the Doctor actually stand in the ruins of Gallifrey; technically bringing the prophecy to pass. Moreover, in this episode, we see hybrids between Time Lords and Cyberman, along with a hybrid Master which destroyed Gallifrey: would that make him the Hybrid ?