Doctor Chaotica is a recurring antagonist in Star Trek: Voyager. He appears in three episodes, debuting in the fifth season opener "Night".
He was portrayed by Martin Rayner.
Doctor Chaotica was the villain of a series of 1930s science-fiction serials, which were recreated by a holodeck programme. Tom Paris was fond of taking on the role of the serials' hero, Captain Proton, with Harry Kim playing his sidekick Buster Kincaid.
The holodeck programme was running when a group of photonic aliens stumbled across Voyager. Unaware of the existence of organic life, they believed the holo-programme to be reality and Voyager to be an illusion. Chaotica's forces captured the first two aliens to arrive and Chaotica killed one of them in cold blood, triggering a war between him and the aliens. With the crew unable to shut down the programme, the aliens' attack were in danger of destroying Voyager. The crew thus decided to end the situation by playing out the holo-scenario and helping the aliens defeat Chaotica. Janeway took on the role of Queen Arachnia, of the Spider People, the object of Chaotica's desires and convinced him to lower the "lightning shield" protecting his death ray. Paris and Kim, with aid from the Doctor, were thus able to launch an attack. Chaotica apparently perished when he was caught in the feedback from the destruction of the death ray, but in true 1930s serial style, the programme ended with a caption reading "The End?" and an evil laugh.
Sure enough, when Voyager was splintered into several different time periods by an accident, the holodeck was shown to be working a Captain Proton storyline with Chaotica as the villain. He was encountered by Chakotay and a Janeway from an earlier time period, who Chaotica recognised as Arachnia. The pair managed to convince him to let them modify the holodeck systems by warning of an attack by aliens from the Eighth Dimension.