Alex O'Loughlin is an Australian actor, writer and director, who plays Lieutenant Commander Steve McGarrett on CBS' remake of the TV series Hawaii Five-0. He had starring roles in the films Oyster Farmer (2004) and The Back-up Plan (2010), as well as on such television series as Moonlight (2008) and Three Rivers (2009).

O'Loughlin was born on 24 August 1976, in Canberra, Australia, of Irish and Scottish descent.His father is a physics and astronomy teacher in Sydney and his mother is a nurse.