In Diablo II, what unique ring became a widely used player-trading currency?

In Diablo II, the Stone of Jordan became a widely used player-trading currency.

The Stone of Jordan is a unique ring that provides bonuses to maximum mana and skill levels. Its compact combination of useful effects made it valuable to many character builds, especially during the early Diablo II economy.

Players also used it as a convenient standard for comparing the value of other items. This practice became so common that the ring functioned like money in player-to-player trading, rather than merely as equipment. Its importance was reinforced by its role in summoning the mysterious Uber Diablo event on Battle.net servers: selling Stone of Jordan rings to merchants could trigger the event in certain versions.

The Stone of Jordan is often confused with other popular unique rings, such as Nagelring and Manald Heal. Those rings can be useful, but neither became the defining currency item of Diablo II’s early trading culture.