The origin of the Defenders lies in two crossover story arcs by Roy Thomas prior to the official founding of the team. The first, in "Doctor Strange" #183 (November 1969), "Sub-Mariner" #22 (February 1970), and "The Incredible Hulk" #126 (April 1970) occurred due to the "Dr. Strange" series being canceled in the middle of a story arc, leaving Thomas no choice but to resolve the storyline in other series that he wrote. In the story, Dr. Strange teams with Sub-Mariner and the Hulk to protect the Earth from invasion by Lovecraftian interplanar beings known as the Undying Ones and their leader, the Nameless One. Barbara Norriss, later the host of the Valkyrie, first appears in this story. In the second arc, featured in "Sub-Mariner" #34–35 (February–March 1971), Namor enlists the aid of the Silver Surfer and the Hulk to stop a potentially devastating weather control experiment, inadvertently freeing a small island nation from a dictator and facing the Avengers under the name of the "Titans Three".