Terrible Zodin

The Terrible Zodin was encountered by and reminisced about by the Doctor on a number of occasions. He first met her some time prior to or during his second incarnation. Iris Wildthyme also claimed to have met her.

Origin
The Terrible Zodin was originally a sword-swallower at the Grand Festival of Zymymys Midamor. (PROSE: Lungbarrow)

Encounters with the Doctor
Zodin was involved in an adventure in which the Doctor interacted with multiple incarnations of himself. After this she erased their memories of the incident using "mind rubbers", preventing the later Doctors involved from remembering having experienced the events before. (PROSE: Cold Fusion)

This did not prevent the Seventh Doctor from remembering enough of the affair to frequently bore people to sleep with long-winded accounts of it, although he was incapable of recalling whether she was assisted in her schemes by mutant kangaroos or by giant grasshoppers. (PROSE: Legacy)

Jamie McCrimmon (PROSE: The Colony of Lies) and Melanie Bush both experienced the incident. (PROSE: Millennial Rites)

When the Doctor's second incarnation visited a UNIT reunion in the early-mid 1980s, he described Zodin to Brigadier Lethbridge-Stewart and indicated the Brigadier would have his own encounter with Zodin alongside the Doctor in his personal future. (TV: The Five Doctors) The Brigadier, however, may have assisted Iris Wildthyme against Zodin in a different matter on the planet Mars. (PROSE: Verdigris)

The Third Doctor disputed that ever took place, (PROSE: Verdigris) although he conceded that accounts of his own conflict with Zodin might not be entirely accurate when confronted with the implausibility of her motives and of grasshoppers jumping eighteen-storey buildings. (PROSE: Legacy)

During the early 21st century, the Terrible Zodin hired a planet assassin named Dominicus to destroy Earth. On that occasion, the Sixth Doctor described her as "a devastating of dissimulation, the queen of corruption and chicanery." (AUDIO: Power Play)

The Eighth Doctor mentioned having the autograph of the Terrible Zodin. (COMIC: The Glorious Dead)

Appearance
The Terrible Zodin had claws, or talons. (PROSE: The Colony of Lies)

Personality
The Seventh Doctor once described Zodin as a celebrated sword-swallower at the Grand Festival of Zymymys Midamor and by no means any kind of actual villain. (PROSE: Lungbarrow) However, the Sixth Doctor considered her a villain of rare guile and cunning. He said they didn't make "villains like her any more". At one point his unstable memory caused him to call Peri Zodin. (TV: Attack of the Cybermen)

The Sixth Doctor thought that she had egomaniacal and megalomaniac tendencies. (PROSE: Millennial Rites)

Behind the scenes

 * The first reference to the Terrible Zodin occurs in a scene in The Five Doctors when the Second Doctor mentions her to the Brigadier. Because several variant cuts of The Five Doctors exist and because Patrick Troughton apparently elaborated on the script, the amount of details on her and the details themselves vary from version to version.
 * The Terrible Zodin has become something of a running joke in Doctor Who. She is always discussed, but so far has never actually appeared on screen, in an audio or in print.
 * The Doctor and Martha Jones at some point met the Terrible Zodin (Martha Jones Blog July 1)