Damian Mackle is a professional wrestler from Northern Ireland, currently signed to WWE, competing on the NXT brand under the ring name Killian Dain as part of the Sanity stable. He previously competed on the independent circuit under the ring name Big Damo, which is derived from his first ring name Damian O'Connor. Prior to joining WWE he was perhaps best known for his work with Insane Championship Wrestling, where he won the ICW World Heavyweight Championship. He also wrestled for numerous promotions on the British independent circuit, around Europe, and in the USA including Progress Wrestling, Revolution Pro Wrestling, Westside Xtreme Wrestling, Absolute Intense Wrestling, Beyond Wrestling, Premier British Wrestling, Scottish Wrestling Alliance, WCPW (now Defiant Wrestling) and IPW:UK. On 19 October 2016, it was announced by WWE that Mackle had signed a developmental contract with the company and had arrived at the WWE Performance Center in Orlando, Florida