Given this paragraph about Riot Games' history, which game was used an indication that games could be supported and monetized long-term?

Context: Riot Games' founders Brandon "Ryze" Beck and Marc "Tryndamere" Merrill became friends while roommates at the University of Southern California, where the two studied business. Beck and Merrill believed too many video game developers diverted their focus from game to game too often, distinguishing Defense of the Ancients as an indication that games could be supported and monetized long-term. They also drew inspiration from Asian video game designers who released their games for no up-front cost and instead charged for additional perks.

Answer: Defense of the Ancients (DotA)