Defense of the Ancients (DotA) is a multiplayer online battle arena mod for the video game Warcraft III: Reign of Chaos and its expansion, Warcraft III: The Frozen Throne, based on the "Aeon of Strife" map for StarCraft. The objective of the scenario is for each team to destroy the opponents' Ancient, heavily guarded structures at opposing corners of the map. Players use powerful units known as heroes, and are assisted by allied heroes and AI-controlled fighters. As in role-playing games, players level up their heroes and use gold to buy equipment during the mission.
The scenario was developed with the "World Editor" of Reign of Chaos, and was updated upon the release of its expansion, The Frozen Throne. There have been many variations of the original concept; the most popular being DotA Allstars, which eventually was simplified to DotA with the release of version 6.68. This specific scenario has been maintained by several authors during development, the latest of whom is the anonymous developer known as "IceFrog" who has developed the game since 2005.
Source: Wikipedia, "Defense of the Ancients," available under the CC-BY-SA License.