In 1985, there was "The Two Doctors". In 2017..."The Two Masters"?
The official Doctor Who site has confirmed that John Simm is reprising his role as the Sixth Master in Doctor Who Series Ten. The specific episode(s) was not revealed, although the two-part Series Ten finale written by Steven Moffat seems most likely.
"I can confirm that it’s true," said Simm, "thanks to the power of time travel, I’m back. It’s always a pleasure to work with this great team of people and I can’t wait for you all to see what the Master gets up to in the next series."
Added Moffat, writer and executive producer, "Nothing stays secret for long on Doctor Who, but you'll have to wait a little bit longer to see exactly what the Master is up to and how he makes his return to face the Doctor. It’s been a huge pleasure to have fan favorites John Simm and Michelle Gomez face to face in the same role! It’s not often you get to see a solo personality clash."
Simm debuted as the Sixth Master in 2007 at the end of the Series Three episode "Utopia", having regenerated from the Fifth Master, played by Sir Derek Jacobi. The story continued in "The Sound of Drums" and "Last of the Time Lords", where the Tenth Doctor (David Tennant) made his way back to Earth to find the Master became Prime Minister of the United Kingdom under the alias of Harold Saxon. As Saxon, the Master remained haunted by a constant drumbeat in his head and he enslaved the world, forcing the Doctor's companion Martha Jones (Freema Agyeman) to spend a year working on an elaborate plan to defeat him. After being fatally shot by his human wife, Lucy Saxon (Alexandra Moen), the Master refused to regenerate, knowing it would haunt the Doctor.
The Sixth Master returned again in 2010, as part of the final Tenth Doctor story "The End of Time", when his disciples attempted a resurrection ritual using a surviving piece of the Master's body. However, Lucy interrupted the ritual, bringing the Master back as a manic undead creature, hungry for human flesh and leaking electrical energy. The Master proceeded with a plot to transform the entire human race into his own clones, and using their combined presence, triangulated the "drumbeat" inside his head to its source -- The Time Lord President Rassilon (Timothy Dalton). The Time Lords, having set up the signal as a means to escape the last days of the Time War, returned to the universe. Confronted with Rassilon, whose drumbeat was the cause of the Master's insanity, the Master teamed up with the Doctor to destroy them. As a result, he was also sent back to Gallifrey with the Time Lords, who were locked away in the Time War and trapped once more.
Doctor Who Series Ten will also feature Michelle Gomez returning as Missy, the Seventh Master known as the Mistress. Other returning foes include the Daleks, the Ice Warriors and – returning for the first time in over 50 years – the Mondasian Cybermen.
Doctor Who returns to BBC One and BBC America for Series Ten on Saturday, April 15th.