Whoo, boy, this is gonna be something interesting...
When I was a little boy, I'd say around three or four, I watched Chuggaconroy's, a youtuber that did walkthroughs with commentary on various classic console games, walkthrough on Super Mario RPG. Whenever I was a kid, I was highly influenced by what I watched, or simply played a game about. Because that game was my favourite game at the time, I decided to name myself, "SupahMatthewRPG," as a username. After I played a game when I was like five, or something, I forgot the name, but I know it had mining moles in it with various types of pickaxes and was a browser game, and its username character limit was less than how long my username was, so I shortened it to just, "MatthewRPG," instead.
And I'm still using it.