Which game is widely credited with popularizing microtransactions in Western gaming markets?

The gaming industry has undergone massive transformations in how companies monetize their products. One of the most significant shifts in gaming revenue models was the introduction of microtransactions - small purchases made within games for virtual items, cosmetics, or gameplay advantages. Test your knowledge about this pivotal moment in gaming retail history that revolutionized how games generate ongoing revenue and player engagement.

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Team Fortress 2 (2007) with its cosmetic hat system
World of Warcraft (2004) with its subscription model
The Elder Scrolls IV: Oblivion (2006) with its horse armor DLC
Second Life (2003) with its virtual land purchases