It was made by the third (3rd) maintainer of Dota Allstars, the warcraft 3 mod. Eul was first, Guinsoo was #2. It had quite a large community attached. Valve hired Icefrog. Icefrog did not invent MOST of the characters, IP, nor mechanics, nor design the map. He DID balance a lot of the characters and interactions. I was an admin for Team Dota Allstars at the time and helped run the semiprivate leagues on battlenet and the dota-allstars forums.
So Valve hires Icefrog, makes an IP claim for the dota name, all the characters, and starts creating dota 2. It felt like a "oh, I'll have this". It didn't feel right at all at the time. Still doesn't. Nothing was ever said for the community that formed around creating and enjoying the game in the first place.
https://dota2.gamepedia.com/Defense_of_the_Ancients