The Karkus was a fictional superhero who was the protagonist of a comic strip which appeared in the Hourly Telepress in the year 2000. The Karkus possessed superhuman strength and an anti-molecular ray disintegrator, wore a cowl and a short cape, and spoke in a German accent. Zoe Heriot was a fan of the strip.
The Second Doctor and Zoe encountered the Karkus in the Land of Fiction. After Zoe defeated him in unarmed combat, he assisted them in their battle against the Master of the Land. (DW: The Mind Robber)
The adventures of the Karkus were still running in the 2050s. (EDA: Alien Bodies)
He never left Zoe Herriot's side when she was the mistress of the land of fiction. He went on a suicide mission to place a book worm in the cyber planner. (BFA: Legend of the Cybermen)