Lumpy Space Messenger first appears in "The Monster." Lumpy Space King and Queen send him to deliver a basket of Lumpy Space Princess' favorite sandwiches to Finn and Jake. He uses a holographic device to project an image of the Lumpy Space King and Queen telling Finn and Jake to find their daughter and bring her home. He speaks with a British accent.
Lumpy Space Messenger is a blue-purple color. He has a yellow crescent moon symbol on his forehead, similar to the stars on Lumpy Space Princess and her parents' foreheads. This most likely shows that he is a royal messenger, servant, or butler to Lumpy Space Princess's family (other lumpers have no such marks).
Sir! My sir!