Complex sentence: Cryptanalysts were selected for various intellectual achievements, whether they were linguists, chess champions, crossword experts, polyglots or great mathematicians, hence their referring to GC&CS as "the Golf, Cheese and Chess Society".
Split into simpler sentences: Cryptanalysts were selected for various intellectual achievements, whether they were linguists, chess champions, crossword experts, polyglots or great mathematicians. GC&CS was ironically referred to as "the Golf, Cheese and Chess Society".