Mark Rosenfelder is a famous conlanger and conworlder. He created the fantasy world Almea with many well-elaborated conlangs, of which Verdurian is the most thoroughly worked out one.
Rosenfelder has authored many books on the art of conlanging and conworlding, including The Conlanger's Lexipedia. He publishes these from his own publisher, Yonagu Books.
Among his most famous books is the Language Construction Kit (LCK), which originated as a fairly short essay on his website.
He is also the head admin of the Zompist Bulletin Board.