Dota is originally a custom map for Warcraft III made by IceFrog. The game quickly became very loved by players all around the world. Dota was special in the way that the game genre was new and groundbreaking. The MoBA (Multiplayer online Battle Arena) concept was invented with the first version of the map and now, several years later there are multiple games in the MoBA genre like Smite, Heroes of Newerth, Heroes of the Storm etc.
Dota as an eSport
As long as there has been computer games there have been competitive gaming. The concept of eSports however did not really develop until the game quake. After that there were competitive gamers labeled as eSports fanatics focusing on several different games like Counter-Strike, Quake, Team Fortress, Starcraft and more. Dota as an eSport was a natural development as the game became super popular quickly. Clans/Teams where created and matches where played five versus five. eSports fanatics devoted there life to the game and stars were born. All this made the dota 2 community grow really big with sites like GosuGamers, JoinDota and TeamLiquid Dota wiki.
The Dota2 eSports boom
The eSports boom came in 2011 together with the launch of Starcraft II and even more so with the livestreaming services like livestream, ustream, own3d and justintv (Now known as the super popular streaming site Twitch.tv). When the interest for Starcraft cooled off a bit the newly released game Dota 2 by Valve (and IceFrog) took over the eSports train. The game was available as a free beta for a long time but was released on the 9th of July, 2013. This raised the awareness of eSports in general and tournaments have been shown on live television. More factors contributed to the eSports boom. Companies really understood the marketing value in eSports and its huge crowd. This made a huge impact for the eSports scene as it was easier to get Sponsors for teams, tournaments where getting bigger prize pools. As an addition to this the betting companies understood that there was an interest from the eSports fanbase to bet on eSports matches.