He's not the author, but he's "the face of Dota" at this point.
(Well, he's "the person of Dota", at least. Mr. Ismail is far too reclusive to ever show his face.)
Unfortunately, it pains me to say this, but this is the truth: If you tried to commercially release your own DOTA, and if you'd copied skills/heroes/items from the original game, Valve, or rather Ismail, would sic lawyers on you immediately. I know this because they tried to do it to S2, the creators of HoN (a very similar game).
So it's unfortunately not true "There really is no rights holder to the game". Valve/Icefrog hold all the cards at this point.
Valve may have creative rights on the details, but I'd be surprised if they could convince a judge that they own the rights to a whole genre of gaming. Especially when there's already a plethora of popular games already under it.
True, however, the details are DOTA. League of Legends isn't DOTA at all, for example.
It's hard to explain. You could only really understand if you'd played the game. "DOTA" roughly means "A highly/specifically competitive game, wherein that game also includes specific heroes and items which competitive players have spent years practicing with and the community in general have come to expect". For example both DOTA and HoN have an item which grants you 10 seconds of magic immunity on use, and can't be used again for more than 1 minute. So if your game doesn't, then it's probably not "a DOTA".
HoN and DOTA both share about ~75% of the "details" (and almost 100% of the details that matter) so it's very much "a DOTA". Whereas League of Legends shares maybe 5%.
(Well, he's "the person of Dota", at least. Mr. Ismail is far too reclusive to ever show his face.)
Unfortunately, it pains me to say this, but this is the truth: If you tried to commercially release your own DOTA, and if you'd copied skills/heroes/items from the original game, Valve, or rather Ismail, would sic lawyers on you immediately. I know this because they tried to do it to S2, the creators of HoN (a very similar game).
So it's unfortunately not true "There really is no rights holder to the game". Valve/Icefrog hold all the cards at this point.