John O'Callaghan is an Irish musician and DJ, who mainly produces trance music. He also produces music under the aliases of Joint Operations Centre, Mannix, Henrik Zuberstein, and Stenna. He has collaborated with fellow Discover artists such as Bryan Kearney, Neal Scarborough (as Inertia), Thomas Bronzwaer (as Lost World), and Greg Downey as well as, more recently, trance hero Leon Bolier. His best-known tracks are "Exactly" with Bryan Kearney, "Big Sky", in collaboration with vocalist Audrey Gallagher, and "Find Yourself" (feat. Sarah Howells). Callaghan has received remixes by trance artists such as The Thrillseekers, Sean Tyas, Gareth Emery, Cosmic Gate, Markus Schulz and Indecent Noise. He has also worked with Heatbeat and Aly & Fila.

Source: Wikipedia (https://en.wikipedia.org/wiki/John_O%27Callaghan_(musician))