League of Legends is a game inspired by the Defense of the Ancients (DotA) map for Warcraft III: The Frozen Throne developed and published by Riot Games for Microsoft Windows and Mac OS X. It was first announced on October 7, 2008 and released on October 27, 2009. The game was in a closed beta from April 10, 2009 to October 22, 2009. It then transitioned to open beta until release.

Steve "Guinsoo" Feak, the previous designer of the popular Warcraft III: The Frozen Throne custom map, DotA Allstars, and Steve “Pendragon” Mescon, the administrator of the former official support base for the map (www.dota-allstars.com), were involved with Riot Games in the development of League Of Legends. Using the original DotA created by Eul (the original Defence of The Ancients map for Warcraft III: Reign of Chaos) as a base, Guinsoo made DotA Allstars by inserting his own mix of content, largely expanding the number of the heroes, and adding recipes, numerous items and various gameplay changes. Guinsoo then passed version 6 of the map on to its current developer, Icefrog. Pendragon, who is the Director of Community Relations for Riot Games, helped create the previous DotA Allstars website along with its forums.

Players are formed into 2 even teams with 1-5 champions on each team. Each team starts at opposing sides of a map, near what is called a "Nexus". A match is won when either the opposing team's Nexus is destroyed or the other team surrenders. To destroy a Nexus, each team must work through a series of towers called "Turrets". Turrets are often placed along a path to each base referred to as a "Lane". Along the way, each player must gain levels from killing the opposing team's "Champions" and "Minions" (small NPCs that constantly spawn and attack the other team) and defeating neutral monsters (some of which grant buffs known as Crests upon death). Also, champions purchase "Items" with in-match gold to improve their champion. In League of Legends, each player starts at level 1 at the beginning of the match and can obtain the maximum of level 18 with their champion, leveling 4 different champion-specific abilities.