K is for... Kronos

Kronos was a Chronovore - a powerful entity which existed outside of Space and Time, but fed on the latter.

When it encountered the peoples of ancient Atlantis it offered them great prosperity. However, its gifts came to be resented as the people grew indolent, lacking any will to work when everything could be given to them for no effort. Like the Gods of Olympus, Kronos could be fickle. When a councillor asked for great strength he was made into a minotaur - half man, half bull. Eventually the rulers of the city decided to put an end to Kronos' influence. They had it imprisoned - the key being a trident-shaped crystal kept in the Temple of Poseidon. The minotaur was employed to guard this.

In the 20th Century the Master decided to capture Kronos himself and harness its power. He obtained a shard of the crystal and built a machine that would allow Kronos to break free. It appeared momentarily as a huge, white winged creature. It caused one of the lab assistants to age by decades in seconds, and could stop time altogether in the local area.

After bringing the High priest Krasis to the 20th Century to help him, the Master realised he would have to go back in time to ancient Atlantis and access the original crystal at source.

On being released, Kronos destroyed the city in revenge for its long captivity.

The creature then took to the Vortex where it encountered the TARDISes of the Doctor and the Master. They had been about to collide but Kronos stopped their destruction. It wished to thank the Doctor for his help, and to punish the Master for his attempts to enslave it. It took on the appearance of a beautiful young woman, and explained that it could take on any image it chose.

The Doctor asked for leniency for his old foe, and the fickle Kronos simply allowed him to go free.

Played by: Marc Boyle and Ingrid Bower. Appearances: The Time Monster (1972).

• Boyle was a stunt man, and he played the white costumed Kronos - whose helmet was based on a Trojan soldier's - as the part entailed being suspended from a harness. Bower played the female version, whose face only is seen in the final episode. Producer Barry Letts, who had co-written the story, was unhappy with both realisations.
• The Chronovores never returned to the programme but have featured in spin-off material - most notably the Sixth Doctor book The Quantum Archangel, by Craig Hinton. This attempts to make sense of the conflicting histories of Atlantis (since sorted out by Steven Moffat).
• In Greek mythology Kronos was the father of Zeus. A Titan, he ate his children after a prophesy claimed they would supplant him. He was tricked into eating a rock instead of Zeus, however. Zeus then overthrew him and freed all his eaten siblings, including Poseidon. They then became the Gods of Olympus.