Thurston Howell IV is the son of Thurston Howell III and Eunice Wentworth Howell with mannerisms and traits identical to his father. Not much is known about his life as nothing is mentioned about him during the time his parents were on the island (At one point, Lovey even claims they don't have a son.), but it is possible he was keeping Howell Industries going in his father's absence as his father's most logical heir, even through the bankruptcy hoax and the discovery of his father's impostor sometime later. In 1981, he is staying on the island in his father's absence as J.J. Pierson attempts to con the former castaways out of their rights on the island.
- Thurston Howell IV was played by TV actor and host David Ruprecht.
- The character was added in, because Jim Backus, who was suffering from Parkinsons's Disease, was too ill to reprise his role in The Harlem Globetrotters on Gilligan's Island, except for a brief cameo towards the end.
- In My Fair Gilligan, Mrs. Howell actually mentions out loud, "Thurston, we haven't got a son." While it is apparent the Howells were not meant to have had children at this point, it is possible (as inconceivable as it sounds) that young Thurston spent so much time in private schools that Mrs. Howell mocked Mr. Howell with his absence that it entered into her behavior (although he would have to humor her to keep from fighting with her over it).
- As David Ruprecht was in his early 30's, when playing Thurston Howell IV in 1981, he would've been in his teens during the original series.