Unless you're British or a relative (or genuine) old-timer, you're probably unfamiliar with Jonathan Penrose. His OTB chess career was relatively short - he stopped playing in his early 40s - but during that period he managed to win 10 British Championships, won two silver medals on first board in Olympiads, and did this as an amateur. (Like his famous father and siblings - most notably Nobel Laureate in physics Roger Penrose - he was an academic, lecturing in psychology.) Among his famous scalps he defeated Bogoljubow and Tartakower when he was a teenager, and in the 1960 Olympiad he gave reigning World Champion Mikhail Tal his only defeat (this is by far Penrose's most famous game), and also defeated former champion Max Euwe as well. He "only" became an IM during his career, though FIDE awarded him the GM title many years later, in 1993.
Whatever one thinks of semi-honorary GM titles, there is no disputing his achieving the GM title in correspondence play, which he took up after concluding his over-the-board career. He never won the World Correspondence Chess Championship, taking third in the 13th Championship (which ran from 1989 to 1998; I assume that counts preliminaries and not just the final), which may have been his only time participating in a correspondence world championship. (It does seem to be his only appearance in a final.) He was apparently the highest-rated correspondence player in the world at one time (possibly at or around the time of the aforementioned 13th Championship, where he, along with Donatas Lapienis, was the top seed), and led the British team to victory in the ninth correspondence chess Olympiad.
All in all, a very accomplished individual, and a notable member of an insanely accomplished family. He passed away a week or so ago, on November 30, at the age of 88. Condolences to his friends and family; may he rest in peace.
For more on his chess career, see this article (which was the source for many of the facts above), along with his Wikipedia page (with links to the pages of some of his extraordinary relatives).