This is a society for people who appreciate Stephen Briggs.
Once upon a time, director of a team of amateur actors Stephen Briggs was pointed towards the Discworld books by Terry Pratchett. He read them. He contacted PTerry. He's adapted them for the stage ever since.
He hasn't kept it to the plays alone. He's been the driving force behind the creation of the Discworld maps and the Companion. Since a job on some UU scarfs got out of hand, he's also maintained one of the first Discworld merchandising websites, CMOT Dibbler.
Yet, he's best known for impersonising Lord Vetinari, the Patrician of Ankh-Morpork, on stage as well as at various Discworld gatherings, the best known of which are the Conventions.