The Shitty Wizard is an inside joke within the Valve staff. It refers to a single person who is "responsible for all Dota 2 bugs". Adrian Finol, a senior programmer at Valve, is the inspiration for the character.
Dota 2 contains many references to the Shitty Wizard. He is mentioned in a voice response line by every hero. The couriers Dolfrat and Roshinante, Garrad Drywiz and Garactacus, Hwytty & Shyzzyrd are ostensibly modeled after him.
All heroes in Dota 2 have voice responses in reference to the Shitty Wizard.