Conor McGregor held UFC titles in two weight classes simultaneously: featherweight and lightweight. He achieved this feat when he defeated Eddie Alvarez for the lightweight title at UFC 205 in 2016. Prior to this, McGregor had already held the featherweight title, which he won by knocking out Jose Aldo in just 13 seconds at UFC 194 in 2015. McGregor's achievement of holding two UFC titles at the same time cemented his status as one of the greatest mixed martial artists of all time.