Defense of the Ancients (DotA) is a multiplayer online battle arena (MOBA) mod for the video game Warcraft III: Reign of Chaos (2002) and its expansion, The Frozen Throne (2003).

[5] Because the gameplay revolves around strengthening individual heroes, it does not require the focus on resource management and base-building found in most traditional real-time strategy games.

[9] Blizzard Entertainment's 1998 real-time strategy game StarCraft shipped with a campaign editor that allowed players to create custom levels, complete with scripted triggers.

Warcraft III also featured powerful hero units that leveled up and could equip items to boost their abilities, and the World Editor enabled mapmakers to create their own.

[11] Taking inspiration from Aeon of Strife and using the expanded capabilities of the World Editor, modder Kyle "Eulogizing" Sommer created the first version of Defense of the Ancients in 2003.

[12] After the release of Warcraft III's expansion The Frozen Throne, which added new features to the World Editor, Eul did not update the scenario and made his map code open-source.

Subsequently, the leaders of the DotA Allstars clan, TDA, proposed that a dedicated web site be created to replace the various online alternatives that were infrequently updated or improperly maintained.

[12] IceFrog was at one time highly reclusive, refusing to give interviews; the only evidence of his authorship was the map maker's email account on the official website and the name branded on the game's loading screen.

[18] Clans and committees such as TDA maintained their own official list of rules and regulations, and players could be kicked from matches by being placed on "banlists".

[18] While increasingly popular, DotA Allstars remained limited as a custom map in Warcraft III, relying on manual matchmaking, updates, and containing no tutorials.

[27] The mod's extreme simplification of the real-time strategy formula made it more accessible for players who enjoyed the spectacle of the battles characteristic of the genre, but did not want to manage the demands of trying to control every part of the experience.

[29] Michael Walbridge, writing for Gamasutra in 2008, stated that DotA "is likely the most popular and most-discussed free, non-supported game mod in the world".

[11][35][36][37] It was one of the influences for the 2009 Gas Powered Games title Demigod,[38] with GameSpy summing its premise up as aspiring gods "[playing] DotA in real life".

[42] The MOBA design DotA popularized also made its way into games that deviated from the mod's top-down perspective, such as third-person shooters and side-scrolling platformers.

[11] DotA also typified the MOBA genre's reputation for unfriendly, toxic behavior and difficult learning curve for new players.

[4] In October 2009, IceFrog was hired by Valve to lead a team to develop a standalone sequel to Defense of the Ancients, Dota 2.

[46] The legal dispute was conceded in May 2012, with Valve gaining franchising rights for commercial use to the trademark, while non-commercial use remained open to the public.