Mark O'Brien is a Canadian actor and director best known for his roles as Des Courtney in Republic of Doyle and Tom Rendon in Halt and Catch Fire. He won the Canadian Screen Award for Best Actor at the 8th Canadian Screen Awards for his performance as Terry Sawchuk in the biographical drama film Goalie.

Halt and Catch Fire is an American period drama television series created by Christopher Cantwell and Christopher C. Rogers. It aired on the cable network AMC in the United States from June 1, 2014, to October 14, 2017, spanning four seasons and 40 episodes. It depicts a fictionalized insider's view of the personal computer revolution of the 1980s and the early days of the World Wide Web in the early 1990s. The show's title refers to computer machine code instruction Halt and Catch Fire (HCF), the execution of which would cause the computer's central processing unit to cease meaningful operation.