James MacArthur, who played Danno, the boyish-looking but hard-driving sidekick on the long-running television detective show “Hawaii Five-O,” died Thursday. He was 72.

MacArthur died in Florida of natural causes, his agent, Richard Lewis, told The Associated Press.

For 11 of the 12 years that “Hawaii Five-O” first ran on CBS, MacArthur, as Detective Danny Williams, chased thieves, hit men, swindlers, spies and assorted loonies. His boss was Detective Steve McGarrett, played by Jack Lord, the straight-laced, tight-lipped head of a small, elite police team determined to keep the idyllic islands from turning into a modern Wild West.

When the bad guy was captured, McGarrett would tell his partner, “Book him, Danno!,” which became the show’s popular catchphrase.

Most of the original show’s main actors are now dead. Lord died in 1998; Kam Fong, who played Chin Ho Kelly, died in 2002; and Gilbert Lani Kauhi (credited as Zulu), who played Kono Kalakaua, died in 2004.

The original “Hawaii Five-O” ran from 1968 to 1980, making it one of television’s longest-running crime shows. It was seen in more than 80 countries.