Lum's father, sometimes referred to as Mr. Invader, is an oni alien and a prominent figure in the Urusei Yatsura series. He is the great warlord who initiated the oni invasion of Earth, serving as the leader of the alien forces. Physically, he is an enormous, pudgy oni with a loud and intimidating presence, though he often does not seem fully aware of how fearsome he appears. His personality is marked by a tendency to raise his voice and act boisterous, yet he also shows a goofy side at times. Despite his commanding role as an invader, he is notably submissive to his wife, whom he fears just as much as Ataru fears Lum; this dynamic is highlighted in episodes where she overrules him, such as when she throws him out of the house for objecting to a diet.

His primary motivation is the conquest of new worlds, but his personal concerns often revolve around family matters, particularly his daughter Lum's relationship with Ataru. He appears as a recurring supporting character, most often in episodes that involve the oni family or invasions of Earth. He typically sides with Lum's wishes, though his loud complaints and bluster create comedic tension. His key relationships include his wife, who dominates him; his daughter Lum, whom he cares for deeply; and Ataru, whom he views as an undesirable but eventually tolerated son-in-law. Over the course of the series, his character undergoes minimal development, remaining a consistent comic foil whose intimidating exterior contrasts with his domestic vulnerability. As an oni, he possesses superhuman strength and the ability to fly, and he commands advanced alien technology for interstellar travel and invasion.