Blue Barry is a character that made its first appearance as a target in the Maple Shot minigame. It also appears as a playable character in Slider Scouts.
Sliderday Scout Spotlight
He comes from the Great Mufflin Kingdom where he is known as Prince Blueregard Barry. The king and queen sent him to Slider Camp in hopes that a little adventure would change his disenchanted demeanor. To blend in with the commoners at camp, and hide his royal status, he simply goes by Blue Barry. 
It is the third character to be revealed to have a royal status; the first were Xandra and Xolo.