Before the lagoon and the coconuts, Russell Johnson was busy getting shot down over the Philippines. He flew 44 combat missions in WWII as a B-25 bombardier, broke both ankles when his plane ditched in the sea in 1945, and used the GI Bill to study acting in Los Angeles. Hollywood cast him as a villain almost exclusively. Westerns, bad guys, shoot-em-ups. He played the Professor on Gilligan's Island only after turning the part down multiple times. Three seasons. His dramatic career never quite recovered.
Gilligan's Island ended in 1967, and the typecasting hit immediately. Casting directors told him the public wouldn't believe him as anyone else, and handed roles to someone else. He spent years trying to shake it. He wrote a memoir about the show in 1993, Here on Gilligan's Isle, which tells you something about how much the show defined him even when he didn't want it to. By his final years he'd made peace with the role. The show's been in reruns continuously since 1967, and the Professor was always the only one actually doing anything useful on that island.
Before he played the smartest person on a desert island, Johnson played almost exclusively criminals and outlaws in TV Westerns. The Twilight Zone used him twice, both times for time-travel episodes: one where he tries to stop the Lincoln assassination, another where a condemned man from 1880 lands in modern New York. He grew up in a boarding school for fatherless boys after his dad died in 1932.
Dawn Wells, his Gilligan's Island co-star who played Mary Ann, posted on Facebook: "And the other half of 'the Rest' is gone," a reference to both their characters being billed in the original theme song only as "the rest." Tina Louise, who played Ginger, issued a tribute. TV Land issued a formal statement calling him "the beloved Professor."