Ragnarok Online (Korean: 라그나로크 온라인), often referred to as RO, is a massively multiplayer online role-playing game or MMORPG created by GRAVITY Co., Ltd. based on the manhwa Ragnarok by Lee Myung-jin. It was first released in South Korea on 31 August 2001 for Microsoft Windows and has since been released in many other locales around the world. Much of the game's mythos is based on Norse mythology, but its style has been influenced by Christianity and Asian cultures. The game has spawned an animated series, Ragnarok the Animation, and a sequel game, Ragnarok Online 2: The Gate of the World.   Wikipedia