Evil genius of Tom Paris's black-and-white Captain Proton holoprograms, who became an unlikely threat to extradimensional aliens.
Doctor Chaotica was the arch-villain of The Adventures of Captain Proton, Tom Paris's holodeck homage to 1930s science fiction serials. Played by Martin Rayner, he ruled from his fortress with his henchman Lonzak and his creation Satan's Robot, scheming to conquer the universe and battling Captain Proton and his sidekick Buster Kincaid.
In Bride of Chaotica!, photonic aliens from another dimension entered the program and took its characters for real. Chaotica waged war on them, and because the program could not be shut down safely, the crew had to win by the program's own rules.
Janeway took the role of Arachnia, Queen of the Spider People, to charm Chaotica into lowering the lightning shield around his fortress, allowing Captain Proton to destroy his death ray and end the conflict. The Proton program remained one of the crew's favorite pastimes.