Thunderaan was a prince of the air elementals. During the Elemental Sundering, the Firelord Ragnaros sought to consume Thunderaan. Thunderaan was betrayed by Ragnaros's lieutenants, Baron Geddon and Garr, and struck down by Sulfuras, the legendary hammer of Ragnaros. Thunderaan fell, utterly defeated. The Firelord feasted upon the essence of the Prince of Air, but was unable to consume him entirely.
What little remained of Thunderaan's essence was stored within a talisman of elemental binding. Ragnaros then shattered the talisman in two flawless pieces and assigned it to his two lieutenants.
Thunderaan wields , a legendary sword. Players can obtain this item through a long and very expensive quest chain, starting from a pair of rare drops in Molten Core.
Thunderaan has surprisingly little HP, so downing him should not be a problem for any 40-man raid with experience in the Molten Core or harder instances. Bring some friends to put the numbers over 40, and you're virtually guaranteed success. He can be killed with far fewer people if they're well-geared or patient - 7 or 8 have been confirmed, and a good 5-person group should be able to complete the fight given time.
Thunderaan has a knockback that wipes aggro, but the radius for the knockback is less than the radius at which he's attackable. So long as the tank stays at maximum melee range the knockback should not be an issue. There is also a chain lightning effect that can hit melee attackers, and an area effect lightning attack that most ranged attackers and healers can avoid by keeping their distance.