Anyone familiar with Warcraft 3 knows what DotA is. It was a hugely popular custom map created using the WC3 engine and played over battle.net. It became so popular that the DotA communities and WC3 communities were separated. DotA was practically another game, entirely community driven. It even sparked Basshunter's rise to fame after he sang about it in his remix of Daddy DJ.
But this isn't about what DotA is/was, it's about what it's turned (or turning) into.
Back in 2009, the creators and designers of DotA's gameplay released a game called League of Legends, a spiritual sequel to DotA. The game was created on it's own engine and was intended to be DotA standing alone away from the WC3 engine and battle.net. But during testing, the testers believed that the gameplay was quote "so much fun and so innovative that it represented the spawning of a new genre and deserved to be its own professional game with significantly enhanced features and around-game services." that the developers sought to have it published, and thus League of Legends was born.
That's all well and good right? A group of people created a custom map that went on and evolved into it's own game, should be the end of a happy story. But it's not.
Less than a year later, S2 Games released a game called Heroes of Newerth, a self proclaimed "DotA based game". (legal code for blatant rip off) You might be thinking to yourselves, what's the problem? Sue the balls off them and move on. Well that's the problem. DotA isn't copyrighted. It's a community game, that used Blizzards engine and battle.net. It wasn't something to be copyrighted. The creators didn't "own" it and neither did Blizzard., but without any of them it wouldn't exist. It existed purely our of the joy the creators got making DotA and that the players got from playing it. No one was trying to get rich off it, not even Blizzard. And it was awesome.
But where most people saw awesome, S2 Games saw a money cow waiting to be stolen. Much like how giant school yard bullies steal candy from small children, S2 Games saw the potential profit of ripping of a defenseless group with no legal backing. Easy train to riches incoming for them, except no. They didn't plan on the creators making their own game, beating them to it, and making it better. Nuts to you, S2 Games.
But they aren't the only ones that want to steal the money cow. The more popular company, Valve, also wants in on the action. They're working on their own version of DotA using their source engine. And in the ballsiest "we just don't give a fuck about you" move ever, are calling it DotA, and tried to trademark and copywrite the name. What the fuck? Blizzard's employee Rob Pardo was quoted saying "It doesn't seem the right thing to do. It just seem a really strange move to us that Valve would go off and try to exclusively trademark the term considering it's something that's been freely available to us and everyone in the Warcraft 3 community up to this point."
It's also worth noting that Blizzard released their own version entitled "Blizzard DotA" for Starcraft 2. It looks like Blizzard also wanted to milk steal the money cow and was just being hypocritical. Oh wait, nope. Blizzard (the one company that it would make sense for them to try and make money off DotA) kept true to the idea that DotA once was and offers it for free. And they didn't steal any of the character ideas the original had, they instead use Blizzard characters from all of their games. Blizzard describes it as being similar to Super Smash Brothers, and the demo show cased characters such as Raynor, Kerrigan, and Zeratul from StarCraft, Sylvanas and Muradin from Warcraft 3, the baby Murloc marine Grunty (which was also a vanity pet in WoW), and a Level 80 Elite Tauren Chieftain, their band mascot.
tl;dr: DotA is awesome. Losers tried to steal it and embarrassed their company.