He has a selfish and playful personality and thinks he's helping out the multiverse. He steals things, raids and destroys AUs to name a few things he does. He loves to play jokes, and make snarky teases at his enemies. Canonically, he doesn't get mad until things don't go his way, how he expected it to happen, or when others trigger one of his fears. And although he has a lot of hatred toward non-canon materials regarding Undertale, the ones that slightly deviate from the original annoys him.