Ragnarok Online, 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.

Ragnarok Online is divided into a series of maps, each of which has its own terrain and native monsters, though many monsters are native to multiple regions. Transportation between maps requires loading the new map and monsters cannot travel from one map to another. There are three major nations in Ragnarok Online, the first of which and where all players start is Rune Midgard. The Schwaltzvalt Republic, an industrialized neighbor to the North, was added in Episode 10 and Arunafeltz, a religious nation modeled after a combination of Israel and Turkey is the subject of Episode 11.

A series of other, minor nations also exists, generally modeled after an ancient society in the real world, examples such as Amatsu, which is modeled after ancient Japan, and Louyang, which is modeled after ancient China. Areas from Norse mythology are also included, such as Niffleheim, the land of the dead, and Valhalla, where players can become Transcendent Classes. New map content is constantly being added to game in the form of Episode updates.

Jobs are one of the most important aspects of Ragnarok Online, as the job a player chooses will have profound implications on his or her strengths and weaknesses, both in a party and outside of one. The job system includes a total of 39 different jobs, divided into 6 categories: Novices, Super Novices, First Job Classes, Second Job Classes, Transcendent Classes and Extended Classes. First classes consist of six basic archetypes; Swordman, Magician, Archer, Acolyte, Merchant, and Thief. Each specializes in certain skills, and uses class-specific weapons and gears.

All players start in the game`s first class, the novice. Novices are, as their name implies, largely a tutorial class built for allowing new players to get the general feel of the game. Once reaching a level goal, players can change to one of six first classes, or choose one of the expanded classes, along with Super Novices. Upon reaching another level goal, first classes can then change into one of two second classes. Once the player reaches base level 99 and job level 50, they can elect to "rebirth" their character, and relevel as a transcendent class, which has more skills and a larger number of status points to work with, although the experience curve is much higher. A player will change jobs multiple times over the course of playing, though the number of changes will be determined by choices made by the player.