Reins of the Red Proto-Drake

Source
This item teaches you how to summon the Red Proto-Drake mount. You must complete the Dungeons & Raids achievement Glory of the Hero to receive this reward. As of Patch 5.0.4, it will automatically be added to your mount collection.

When you completed the achievement before Patch 5.0.4, would send you the Drake with the following letter:

Mount Journal
The vrykul were the first to recognize their potential. Or maybe the second, depending on how you look at it.