mariofan888 is notorious for being the creator of 1, 2 Oatmeal. Not much is known about him, except that he's a German Let's Player that has made terrible parody songs from video games.
There is also another related account with more videos called けんしん (KevKevLP), with this account having the English version of 1, 2 Oatmeal. It is confirmed that mariofan888 and KevKevLP are the same people, because their linked Facebook account is the same.
He currently resides on an account called KAZAN, where makes new videos very frequently. (pls subscribe to him he deserves it).
In the video "Tales from Gay Baby Jail: Oatmeal's Revenge", it is revealed that unknown people unleashed him to stop Harry and Emma.