Sticking to his metropolitan hometown for college, Cullen pursued acting at the University of Houston and befriended fellow young actor Dennis Quaid, forming a long-lasting bond. While Quaid rocketed to stardom, Cullen paid his dues on television, landing a mix of small and substantial roles on major network productions. In 1983 he appeared in the heralded miniseries "The Thorn Birds" and later took on the part of Dan Fixx for more than 50 episodes of the popular soap "Falcon Crest." Cullen's Texan ruggedness made him a good fit for Westerns, with a role as Marshal Sam Cain on "The Young Riders" (ABC, 1989-1992) and eventually a starring turn on "Legacy," which only lasted one season despite solid reviews. Prior to this series, he also had a lead part in the sitcom "The Simple Life" (CBS, 1998) with Judith Light, which met an even quicker fate. Already a steady working actor, Cullen became more in-demand in the new millennium, playing a supporting role in the feature football comedy "The Replacements" (2000) and portraying recurring characters on a number of major shows, including "The West Wing," "Lost" and "Friday Night Lights" (NBC, 2006-2011). Often cast as fathers, Cullen played the dad of Nicolas Cage's title antihero in "Ghost Rider" (2007) and also had a paternal turn in 2012's resistance-fighter movie remake "Red Dawn." After briefly appearing in the superhero blockbuster "The Dark Knight Rises" (2012), he joined the cast of the tense drama "Person of Interest" (CBS, 2011-16) as a key character tied to the show's super-surveillance conceit and also became a regular on the soapy dramedy "Devious Maids" (Lifetime, 2013-16).