Nackle Seijin is an alien antagonist from Return of Ultraman, a member of the Nackle alien race. He serves as one of the series’ notable monster-of-the-week style enemies, often acting as a dangerous invader or manipulator behind attacks on Earth. In the show, Nackle Seijin is remembered as a cunning and ruthless foe who schemes against Ultraman Jack and humanity. The character represents the recurring extraterrestrial threat central to the Ultraman franchise.