In which expansion was the 'Looking for Raid' feature introduced?

Looking for Raid was introduced in the Cataclysm expansion. It arrived with Patch 4.3, Hour of Twilight, released on November 29, 2011, near the end of Cataclysm’s content cycle.

The feature, usually abbreviated LFR, was designed to let individual players queue for raid content without already belonging to a coordinated 10- or 25-player group. The Raid Finder automatically assembled a large group and matched players into a more forgiving version of the Dragon Soul raid, Cataclysm’s final major raid.

A common mix-up is confusing the feature’s launch with later improvements. Mists of Pandaria expanded and refined Raid Finder, while later expansions adjusted raid sizes, loot rules, and difficulty. However, the original Looking for Raid system belongs to Cataclysm, specifically Patch 4.3. The feature helped make raid storylines accessible to players who could not commit to scheduled guild runs.