Clark has been described by his creator as "Ryan’s dark side" and "more inclined to take physical action than Jack is." A former Navy SEAL, he became an operations officer for the Central Intelligence Agency, and at one point served as Ryan's driver and bodyguard. During Ryan's first term as President of the United States, Clark served as director of a multinational counterterrorism unit codenamed Rainbow, which is composed of elite soldiers from countries which are part of the North Atlantic Treaty Organization. After retiring from CIA and Rainbow, Clark then worked for The Campus, an off-the-books intelligence organization created by President Ryan, later acquiring a position as director of operations.