Mark O'Brien is a Canadian actor known for his versatile performances in film and television. He gained recognition for his role in the series Republic of Doyle, where he played the character Des Courtney. O'Brien has also appeared in various other projects, showcasing his talent across different genres. In addition to his work on television, O'Brien has acted in films such as The Last Exorcism Part II and Ready or Not. His ability to portray a range of characters has made him a notable figure in the entertainment industry, earning him a dedicated fan base.