Zalgo is a hacker on MovieStarPlanet (UK, and USA). They are known for being rude to their victims before hacking them, using offensive slurs and inappropriate language. Not much is known about Zalgo, but we know they aren't like every other hacker. They definitely don't not like to be thought of as every other hacker and hates to be compared with other hackers.
They were very popular and active on forums, which is where they gained the majority of her fame.
Zalgo is believed to be based off a Creepypasta character who goes by the name of Zalgo. They could also be based off a creepy font by the same name