Hypnotron

The Hypnotron was an enemy which the Fourth Doctor recalled having defeated. (PROSE: The English Way of Death)

Behind the scenes
Among some 250,000 entries, the Hypnotron, created by Paul Worrall, was one of three winners of the Blue Peter's 1967 design-a-monster-competition, along with the Aqua Man and the Steel Octopus. Unlike the later Abzorbaloff, it was not featured in the Doctor Who television series, however, a prop Hypnotron was constructed alongside the Steel Octopus and the Aqua Man. (REF: The Doctors: The Archive)