O'Leary's appearances on "Dragons' Den" and "Shark Tank" popularized the nickname "Mr. Wonderful" for him; he has said that he is often referred to by that name in public. O'Leary has said that the nickname serves both as a tongue-in-cheek reference to his reputation for being mean, as well as a reflection of his view that his blunt assessments are helpful to misguided entrepreneurs. In a 2013 interview, O'Leary implied that he could not remember how he got the nickname. He had already referred to himself as "Mr. Wonderful" in a 2006 casting video for "Dragon's Den", predating either show.