Russell Johnson, who played the professor on “Gilligan’s Island,” died Thursday morning, his agent told TheWrap. He was 89.

Johnson died at his home in Washington state of natural causes, his agent, Michael Eisenstadt said.

Born in rural northeastern Pennsylvania, Johnson graduated from a private boarding school for orphaned children before joining the Air Force, flying dozens of combat missions in World War II – including one that turned him into a real-life castaway in the Philippines in 1945. Johnson’s B-25 bomber was shot down by heavy flak; he broke both his ankles during the mission, and received the Purple Heart.

See photos: Hollywood’s Notable Deaths of 2014

Johnson’s acting career started nearly a decade later, with early roles in westerns and sci-fi movies and TV shows, including “It Came From Outer Space,” “This Island Earth” and “Attack of the Crab Monsters.” His TV career was robust through the late 1950s and early ’60s, including as a regular on “Black Saddle” and two episodes of “The Twilight Zone.”

But he’ll be best remembered as Roy Hinkley – “The Professor” – on “Gilligan’s Island.” Johnson’s unwavering, straight-man treatment of the character brought brains and gravitas to the otherwise silliness of Sherwood Schwartz’s creation; it also afforded the otherwise hapless castaways a badly-needed hero, whose fix-it-with-whatever’s-around approach would give way to more modern characters like Richard Dean Anderson’s “MacGyver” and spurned spy Michael Westen on “Burn Notice.”

See photos: Hollywood’s Notable Deaths of 2013

Johnson was the last surviving male castaway from the TV series that ran from 1964 to 1967. Bob Denver (Gilligan) died in 2005; Alan Hale (the Skipper) died in 1990; and Jim Backus (Mr. Howell) died in 1989. Natalie Schafer (Mrs. Howell) died in 1991; Dawn Wells and Tina Louise (Mary Ann and Ginger) are the last surviving castmembers.

Wells posted photos of Johnson on her Facebook and Twitter feeds Thursday:

My 2 favorite people are now gone. The Professor past away this morning. My heart is broken. http://t.co/32afNb9wrW – Dawn Wells (@therealmaryann) January 16, 2014

A picture of Russell and his lovely wife Connie. Russell was a true gentleman, a good father, a great friend,… http://t.co/CIdOL9OSrM – Dawn Wells (@therealmaryann) January 16, 2014

Johnson’s career had legs after the Island, appearing in more Westerns and sci-fi movies and TV shows including “Gunsmoke,” “Dallas” and the Robert Redford spy thriller “Three Days of the Condor.”

TV Land president Larry W. Jones added, “We are deeply saddened to have learned of the passing of Russell Johnson, the beloved ‘Professor.’ We extend our deepest condolences to his family. ‘Gilligan’s Island’ is one of the most iconic television series in pop culture history. The news about Russell makes its return to TV Land on Monday all the more meaningful.”

He’s survived by his wife Constance Dane, stepson Courtney Dane and daughter Kim from a previous marriage; his son David, an AIDS advocate, died from the disease in 1994.

Tim Kenneally contributed to this story.