Update: We have created list of Dota 2 heroes and guides, please visit it here.
What's a Dota?
Dota 2 takes its name from the Warcraft III mod Defense of the Ancients, a drastic change to that stock real-time strategy title, which pits two teams of five players against each other in highly competitive, 40-minute or longer matches. Unlike most RTSes, DotA has each player controlling a single hero who levels up and stockpiles gold to purchase powerful equipment and consumables. As computer-controlled armies continually spawn and rush the enemy's base, players are responsible for using their powerful heroes to turn the tide of the battle in their favor.
DotA quickly gained massive popularity on Blizzard's Battle.net service, with the growing community utilizing user-created channels and the rudimentary custom game browser to connect players. As mods tend to do, it branched into several variations as time passed. Eventually, one rose to the top: DotA-Allstars, originally created by Steve "Guinsoo" Feak (now employed with Riot Games designing League of Legends). Allstars is currently maintained and updated by IceFrog (who declined to give his real name), who was hired by Valve in 2009 and is now working on Dota 2.