Richard Bartle is best known for having co-written in 1978 the first virtual world, MUD (Multi-user dungeon), and for his 1996 Player Types model (killers, socializers, achievers, and explorers) which has seen widespread adoption by the MMO industry. His 2003 book, Designing Virtual Worlds, is the standard text on the subject, and he is an influential writer on all aspects of MMO design and development. In 2010, he was the first recipient of the prestigious GDCOnline Game Legend award.