From Wikipedia, the free encyclopedia. Dean Winters (born July 20, 1964) is an American actor, who has portrayed Ryan O'Reily on HBO's Oz, Johnny Gavin on FX Network's Rescue Me, and Dennis Duffy on NBC's 30 Rock. He also currently portrays "Mayhem" in Allstate commercials. Description above from the Wikipedia article Dean Winters, licensed under CC-BY-SA, full list of contributors on Wikipedia.​