The 2004 Blizzard game that lets players explore Azeroth in a massively multiplayer online role-playing game is World of Warcraft.
Blizzard Entertainment released World of Warcraft in North America on November 23, 2004. It expanded the Warcraft setting from real-time strategy games into a persistent online world where players could create characters, complete quests, fight monsters, join groups, and interact with thousands of other players.
The game used a subscription model in many regions and quickly became one of the most commercially successful MMORPGs ever made. Its success brought the Warcraft universe to a much broader audience than the earlier strategy titles, Warcraft: Orcs & Humans, Warcraft II, and Warcraft III.
World of Warcraft is not the same game as Warcraft III: Reign of Chaos. Warcraft III is a 2002 real-time strategy game, while World of Warcraft is an online role-playing game set in the same broader fictional universe.