Matthew was a character who appeared in "The Mountain." He was the ruler of a mountain named the Mountain of Matthew. He was the distilled body of all the beings who have completed the mountain. He is now one form of the several beings who have merged into him. In the episode, he was met by Finn and Lemongrab after they complete their obstacles.
Matthew was a humanoid composed of a group of cultist humanoid followers merged together creating one large being. He has the appearance of a cloud with a hole in his left torso. The top of his head carved a hollow dent inside him. His appearance is similar to Little Dude (character)'s. When he is hit by Lemongrab 3's lemonjon candies, he disperses into the dozens of humanoid cultists who formed him in the past.
Matthew was self-dependent and believed, after the "second age of terror", would return to his true form and restore the world through domination after he had distilled enough beings to evolve into his final state. He was also seen trying to merge with Lemongrab in "The Mountain."