Smurfing

The practice of strong gamers playing under another identity (often masquerading as a newbie) is sometimes known as "smurfing". It happens in online games such as Starcraft, and now it has become news in the chess world.
World Champion Magnus Carlsen has engaged in a bit of this recently, winning a number of online events while hiding his identity. Starting off as "DannyTheDonkey" he quickly moved on the "DrDrunkenstein". Under these names (and a few others) he won a number of lichess.com events, often while live streaming the action. Importantly, he didn't try and pretend to be someone else (which may have raised some ethical issues), but simply left it up to others to guess who he was.
"Smurfing" is generally considered OK in the online gaming community, as long as it isn't used to gain an otherwise unfair advantage (eg creating accounts to throw games to other players). Usually it is done as a kind of challenge, where a player starts off with a low ranking and then sees how quickly they gain build it up again. It is even used in games like Poker, where a strong players starts an online account with $1 in it, and sees how long it takes to earn $100,000!
The full glorious story is available here, and is well worth a read. If anything, it may encourage more players to enter events like this, as playing an anonymous Carlsen may just lead to your "fifteen minutes of fame".