MC is the announcer of the Poptropolis Games. He is the person you must talk to in order to enter the games. He seems to be a bit impatient, as evident by his reply when you say that you are not ready yet to enter the games. At the end of the island, he announces the winning tribe.
His name appeared in the concept art for Poptropolis Games.
MC might actually be this character's title rather than name, as MC is short for "Master of Ceremonies", which is a person who introduces people including performers or contestants.