Alex O'Loughlin is an Australian actor, writer, director, and producer, who portrayed Lieutenant Commander Steve McGarrett on CBS' remake of the TV series Hawaii Five-0 (2010–2020). 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 (2007–2008) and Three Rivers (2009–2010).

Steve McGarrett is a fictional character who is the protagonist of CBS' Hawaii Five-O created by Leonard Freeman. McGarrett is a former United States Navy officer and the leader of a special state police task force, which is called Five-O. McGarrett was portrayed by actor Jack Lord in the original show from 1968 to 1980, and later by Alex O'Loughlin in the series' remake from 2010 to 2020. Throughout the show, McGarrett is partner to Detective Danny "Danno" Williams.