The Master's usual mode of operation after he arrives on Earth in season 8 of Doctor Who is to cooperate with another alien power to try to take over the planet, although the details of the cooperation vary a lot from story to story. He works with the Nestenes in "Terror of the Autons," with Axos in "The Claws of Axos," and Azal in "The Daemons."

In his second appearance, the entity the Master is working with is some kind of being that absorbs evil thoughts. It spends practically the entire episode inside a box (the "Keller Machine," after the Master's alias).

The Keller Machine

Initially, it seems like the Master may have created the entire device, but it is soon revealed that the thing inside is a separate intelligent organism, which the Master is losing the ability to control. When the machine is opened up, the thing inside is a slimy-looking ball of goo.

The Alien

However, nothing is ever explained about where this alien actually came from or how the Master came to be in control of it. Is there any more information about the thing somewhere, perhaps in the novelization by Terrance Dicks or somewhere else in Doctor Who lore?

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    The novelization says that "it's from a remote planet on the edge of a far distant galaxy", but doesn't say much more Mar 8, 2022 at 16:38

1 Answer 1


There are no other episodes of Dr Who that mention the mind parasite, however, there is a Big Finish Production audio story that deals with them. "Sympathy for the Devil" by Jonathan Clements is a part of the Doctor Who Unbound series which deals with What If scenarios. In the book, a variant of The Third Doctor was meant to be exiled to the 1970s but instead arrived in 1997. Because of this most of the adventures during the 7th to 11th season didn't happen or happened differently.

The cover to Doctor Who Unbound, Sympathy for the Devil

In this new reality, The Master built the Keller device for the Chinese government, which used it for mind control. When the Doctor confronts the Master about it we learn that the parasites arrived in a starship crash 150 years earlier and at that time The Master took control of all of them except one, which was kept in a temple. Unfortunately, that is all we learn about the background of the parasites, but at least we know that they are not native to Earth or created by The Master.

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    According to tardis.fandom.com/wiki/Keller_Machine, the Seventh Doctor encountered a device which was heavily implied to be a parasite similar to the Keller Machine. in the New Adventure Legacy, but I haven't been able to confirm this.
    – jim
    Mar 8, 2022 at 9:32

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