From what I recall from one of the early "Making of Star Trek" books, the original idea for Sulu was that he had the attention span of a gnat with regards to hobbies. One month he'd be obsessed over fencing, the next month plants, etc. Didn't really get made as explicit as it probably should, particularly as the non-KirkSpockMcCoy characters faded into the background as the show continued.

Tom Galloway