The Wasp Leader is the head of the infamous biker gang known as The Wasps who are in on Rigby's surprise for Eilleen, he appears in the Season 7 episode Crazy Fake Plan.
There is a scene where they try to pass the Wasp Riders which they all grunt and growl. they get past one row, but the second goes and blocks them off. They surround the car and Eileen claims she's scared. The leader comes up to the car claiming they don't fit in and asking what's their business. Rigby Claims he wont tell them after they tie them up with duct tape saying they'll throw them off a cliff.