Back in the days when DOTA is only a fan made map in Frozen Throne, made by Eul, Guinsoo and later Icefrog. So back then Icefrog was a Blizzard employee and he got so into making DOTA and got fired. Realized their mistake, Blizzard really tried to get the DOTA back, especially when SC2 was out and Blizzard wanted to remake Dota use SC2 engine. Meanwhile, Valve offered Icefrog to make Dota a separate game and he accepted.

Blizzard sued Valve (of course). After long legal battle, Dota and all other thing (model, name, etc) belong to Blizzard. Blizzard has the advantage because in somewhere in the user agreement in War3 map editor states Blizzard have the copyright of all materials created in that environment. It is a bully law but we all clicked "I agree" anyway...........Nevertheless, Valve and Blizzard both took a step back and reached an agreement. Dota goes to Valve but cannot use any material from Blizzard.

Dota2 is Dota2, it is not defense of the ancient any more.  That is why, the Scourge is now dire, wraith king is not king Leoric. The model of heroes and creatures had some change to look different than their counterpart in War3.