Mr. Starbeam is one of Dolph's fathers. He was seen bullying Homer by beating him up at Moe's Tavern with Mr. Jones and Mr. Zzyzwicz and accusing him of raising Dolph Starbeam, in "The Homer They Fall".
One of Dolph's fathers is Jewish, sending Dolph to Hebrew school, while the other is a die-hard hippy. However, both of his fathers have anger management issues, as Bart's comical creation 'Angry Dad' talks like they do and it sounds like they may be abusive.
Since Dolph lives with his two fathers, while his mother dates around, it's possible that Mr. Starbeam is bisexual.