Otto Bagman is a minor wizard and the brother of Ludo Bagman. He is mentioned only in Harry Potter and the Goblet of Fire, where his primary role in the narrative is to highlight the depth of his brother's irresponsibility and gambling problems. Otto's ownership of a Muggle lawnmower becomes a point of contention when Ludo attempts to use it to pay off his debts to a group of goblins.
Otto's personal history is largely unknown. He appears in the story indirectly during the 1994 Quidditch World Cup and the subsequent Triwizard Tournament.
Otto's physical appearance is never described in the novels. Based on the limited information available, Otto is portrayed as a victim of his brother's reckless behavior. His anger over the theft of his lawnmower suggests he is more responsible than Ludo. His brother calls him “a bit of a weirdo,” and his ownership of a Muggle artifact he apparently cannot operate properly indicates an eccentric interest in the non-magical world, a trait shared by other wizards like Arthur Weasley.
As Otto never appears directly in the story, his magical abilities, skills, and wand details are unknown.
Otto Bagman is a book-only character and does not appear in the film adaptation of Harry Potter and the Goblet of Fire. There is no additional information about him from J.K. Rowling on Pottermore or in interviews.