Kirin Tor Familiar

Simply speak to Archmage Vargoth to receive this pet. Vargoth is housed in a secluded spire atop the Violet Citadel within Dalaran. In order to access Vargoth, one must teleport to his location using a tome rewarded by the "Higher Learning" achievement. This achievement entails reading 8 different books about arcane magic that spawn throughout Dalaran. The books appear to be on 3 hour spawn timers and share spawn points with roughly 30 other non-achievement books.

Note that while a warlock and two others who have access to Vargoth can summon another player to his location, that player cannot receive the pet without having completed the achievement.