As of April 2014, Shark Boy changed his avatar name to Shark Guy and his username to sharkguycreator. All external appearances of Shark Boy were covered up as well. Read more about the disappearance here.
Shark Guy is a grumpy character - while the first two questions you ask him are answered politely, he soon grows tired of you, and admits that he's not a real shark, and is just a guy trying to make a living. His shark outfit has visible stitches and a shark fin similar to the one you can receive from the Shark Fin Vendor. He holds a fish that is seemingly dead. With relaxed eyes and unhappy smile, he's every kind of melancholy.
You'll find Shark Guy inside the Shark Museum on Shark Tooth Island. He's on the bottom floor, inside a pool of shallow water. When prompted, he will answer your first two questions, and then will tell you that he's just trying to make a living.
In the animated short "Shark Toon", Shark Guy explains why sharks bite humans.
Other than appearing on Shark Tooth Island, Shark Guy is a star in the Poptropica universe, appearing in everything from t-shirts to toys. In April 2014, however, the majority of his appearances and all around evidence of existence were almost completely eradicated. Here is a list of his appearances (mostly now deleted or replaced by another character).