Ann Oldenburg

USA TODAY

We all knew him as simply the Professor.

Russell Johnson, the actor known as the quirky, smart Gilligan's Island character, Professor Roy Hinkley, has died at age 89.

ABC News confirmed with the actor's wife, Constance, that Johnson died Thursday morning of kidney failure.

"He died at home, peaceful, in his sleep at 5:21 am today," she said. "(He was) a very brave guy who knew what he wanted, and he wanted to be at home."

Dawn Wells, who played Mary Ann on the show, posted a note on Facebook, reports TMZ, that said, "My 2 favorite people are now gone. The professor past (sic) away this morning. My heart is broken." She added, "Russell was a true gentleman, a good father, a great friend..."

Gilligan star Bob Denver died in 2005. Alan Hale Jr. died in 1990. And Jim Backus died in 1989.

Originally from northeastern Pennsylvania, Johnson served in World War II before pursuing an acting career. He appeared in several TV programs in the 1950s and '60s, including Alfred Hitchcock Presents and The Twilight Zone. But he was best known for his 98 episodes of Gilligan's Island, which aired from 1964 to 1967.

Johnson, a resident of Bainbridge Island, Wash., leaves behind his wife and a daughter, Kim.