Complex sentence: His genre career began in science fiction fandom in which as a long-time participant he worked on a number of fanzines, notably "Xero", which he edited with his wife Pat and Bhob Stewart.
Split into simpler sentences: His genre career began in science fiction fandom in which as a long-time participant he worked on a number of fanzines. The best known was "Xero", which he edited with his wife Pat and Bhob Stewart.