Atiesh, Greatstaff of the Guardian is a Feat of Strength for equipping a when it was still available.
Patch 3.3.0 (08-Dec-2009): Changed from "completed the quest to obtain " to "wielder of."
Although the quest chain can no longer be started, players on the quest [60R] (or any later quest in the chain) who already have the can still complete the legendary quest chain and get the Feat of Strength. This requires first collecting 40 , begining the quest chain, and killing Kel'Thuzad in the original 40-man version of Naxxramas. If these requirements have been met, the rest of the quest chain is still completable.