Russell Johnson, who was best known as the Professor on “Gilligan’s Island,” died Thursday in Washington state of kidney failure, according to his longtime agent Michael Eisenstadt. He was 89.

From the 1950s through the 1980s, he guest-starred on numerous TV shows including “Twilight Zone,” “Lassie,” “Lou Grant,” “Dynasty” and “Alf.” But Professor Roy Hinkley on “Gilligan’s Island” was his most indelible role on the show that ran from 1964 to 1967.

His character was basically the straight man to the kooky cast of characters marooned on the island. “Gilligan’s Island” creator Sherwood Schwartz once described the character: “Very often the Professor is the one who prevents the rest of the group from taking rash actions. The others look to him and his great store of scientific knowledge, especially as it might affect their possibility of rescue.”

“Gilligan’s Island” had only a short run in primetime but has lived on in reruns for decades. As the 50th anniversary of its debut approaches, the show is getting a big promo push with a run on TV Land that begins Monday.

Castmate Dawn Wells noted that she and Russell jokingly called themselves as “the Rest,” a reference to the lyrics of the show’s famous theme song.

“And the other half of ‘the Rest’ is gone,” Wells said. “Russell was a true gentleman, a dear friend with a fantastic wit and wonderful actor.”

After serving in the Army Air Corps in World War II, he enrolled in acting school. Throughout the 1950s, Johnson appeared in sci-fi films including “This Island Earth” and “It Came from Outer Space.” He was also a frequent Western actor in films such as “Tumbleweed,” “The Stand at Apache River” and “Ride Clear of Diablo.”

Johnson is survived by his wife and a daughter.