The developer of Warcraft III, Blizzard Entertainment, largely opposed the development and branding of Dota 2. They filed an opposition to Valve's trademark, but the ruling was in Valve's favor, effectively transferring the franchise away from Blizzard and to Valve.
Dota 2 is the sequel to the Warcraft III custom scenario Defense of the Ancients, developed by the pseudonymous lead designer, IceFrog. Said lead designer was hired in 2009 by Valve to develop a stand-alone sequel that would be a virtual re-engineering of the original, on the Source engine.