To understand the history of DotA, one must begin from Starcraft. In the early days of Starcraft, there was a UMS (Use Map Settings) map called Aeon of Strife (AoS) made by a modder called Aeon64 that featured a cooperative game with four heroes facing off against endless waves of computer-controlled creeps in four lanes. The players would have endless computer-controlled creeps on their side as well, except these were weaker than the enemy creeps. The familiar game mechanic of the player who last-hit an enemy unit being rewarded with money can be found in this map. The game would end once key buildings on either side were destroyed or with the deaths of all four player-controlled heroes. A second version was made so that four players faced off against each other in a 2v2 fashion with endless creeps on both teams.

Once the Warcraft 3: Reign of Chaos (ROC) was released on July 3, 2002, Aeon of Strife was ported over to ROC where free of the limitations of the Starcraft map editor, a much more interesting game could be made. Players could gain experience alongside money, gain levels, learn more powerful abilities and buy equipment. Many of the game mechanics in modern DotA can be found in maps from this period.The first AoS-styled map that took advantage of the ability to design custom spells provided by the powerful ROC World Editor was Valley of Dissent made by a modder called Karukef. Another modder called Eul borrowed some ideas of his predecessors to create an AoS-styled map called Defence of the Ancients (DotA), which would become one of the most popular UMS maps on Battle.net.