Damian Mackle (born 20 February 1985) is a professional wrestler from Northern Ireland currently signed to WWE, competing in their developmental territory NXT under the ring name Killian Dain. He previously competed on the independent circuit under the ring name Big Damo, which is derived from his original ring name Damian O'Connor.
He is perhaps best known independently for his work with Insane Championship Wrestling, where he won the ICW World Heavyweight Championship. He also wrestled for numerous promotions in the British independent circuit, around Europe, and in the USA including Progress Wrestling, Revolution Pro Wrestling, Westside Xtreme Wrestling, Absolute Intense Wrestling, Beyond Wrestling, WhatCulture Pro Wrestling, Premier British Wrestling, Scottish Wrestling Alliance and IPW:UK. He was also the inaugral WhatCulture Pro Wrestling World Champion.
On October 19, 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.
- 3 Count Wrestling Tag Team Championship
- Insane Championship Wrestling World Heavyweight Championship
- Pride Wrestling Championship
- Reckless Intent Wrestling Hardcore Championship
- Reckless Intent Wrestling Heavyweight Championship
- Scottish Wrestling Alliance Laird of the Ring Championship
- Scottish Wrestling Alliance Tag Team Championship
- Scottish Wrestling Entertainment Heavyweight Championship
- WhatCulture Pro Wrestling World Championship
- World Wide Wrestling League Heavyweight Championship
- World Wide Wrestling League Tag Team Championship
- X Wrestling Alliance British Heavyweight Championship