Actor Russell Johnson, best known as Professor in the 1960s TV sitcom "Gilligan's Island," died Thursday, his agent said. Johnson was 89.

Johnson played the iconic role of Professor Roy Hinkley, whose scientific schemes to get the castaways rescued were always foiled by Gilligan's bumbling.

He died at his home in Washington, where he lived with his wife, Connie. She and their daughter, Kimberly, were at his side, said agent Mike Eisenstadt. Johnson is also survived by a stepson, Court, and a grandson, he said.

Johnson worked up until his death, signing autographs over the holidays, said Eisenstadt. He called Johnson's death "unexpected."

The chief deputy coroner in Kitsap County, Washington, told CNN that Johnson died from natural causes.

Johnson was "just a positive and nice guy" who always treated people with respect, his agent said.

His acting career began in the early 1950s with many jobs as a character actor on television. He played Marshal Gib Scott in two seasons of "Black Saddle," a Western that ran in 1959 and 1960.

Johnson acted in dozens of television shows after the four seasons on "Gilligan's Island," but his career seemed stranded on its own island because of the popular sitcom role.

A noteworthy big screen role was as a nuclear physicist in the 1955 science fiction film "This Island Earth."

Johnson was in Ray Bradbury's 1953 sci-fi classic "It Came From Outer Space."

Before becoming an actor, Johnson served in the U.S. Army Air Forces during World War II. He was on a B-24 Liberator when it was shot down during a bombing raid over the Philippines in 1945, according to his official biography, and used his G.I. Bill benefits to pay for acting school after the war.

Johnson, in a 2004 interview for the Archive of American Television said the success of "Gilligan's Island, which he never expected to last more than the initial order of 13 episodes, was the result of the "great chemistry" of the cast.

Tina Louise, who played the glamorous Hollywood starlet Ginger on "Gilligan's Island said she was " very saddened to hear of the passing of Russell Johnson."

"My prayers and condolences go out to his wife Constance and his family," Louise said. "He will always be in our hearts and remembered from Gilligan's island as part of American pop culture history. He will truly be missed."

Johnson's advice to young actors was to "prepare yourself."

"Most of us have to really learn how to do what we do, and that takes some studying and being part of an acting group," he said. "Preparation is everything, and that means studying."

Another important ingredient to acting success is perseverance, he said. "You can have all the talent in the world, but if you don't persevere, if you don't stick to it, it doesn't mean anything."