Kotaku sums up the history rather nicely: Blizzard made a game called Warcraft 3: Reign of Chaos and then released an expansion pack called The Frozen Throne, the latter of which was the foundation for a popular mod called Defense of the Ancients (DOTA). Half-Life 2 creator Valve then decided to develop a stand-alone sequel to DOTA called DOTA2. Meanwhile, Blizzard created a StarCraft 2 multiplayer map called Blizzard DOTA. Now the two developers are battling head-to-head over the DOTA name.
The fight actual stems back to 2010.
2DayBlog.com, Blizzard and Valve at War Over DOTA Name
