The 5 Ring

The 5 Ring can be found rarely inside the Tiny Titanium Lockbox, itself found extremely rarely inside the Bag of Fishing Treasures (Dalaran) rewarded from completing Marcia Chase's daily fishing quests in Dalaran.

Trivia

 * Direct reference and humorous variations on The One Ring, the most powerful item in Middle-Earth, which drives the plot of Lord of the Rings.