Leokk

Leokk is a wyvern found in Blade's Edge Mountains. He is one of several beasts belonging to Rexxar.

The Burning Crusade
Shortly after Rexxar arrived in Blade's Edge Mountains, he was attacked by Bladespire ogres. Although Rexxar escaped after slaying many, Leokk was taken prisoner. Thankfully, with the help of Spirit and a Horde adventurer, Leokk was located and freed.

Legion
Leokk can be seen flying overhead in Trueshot Lodge, even before Rexxar arrives.

Trivia

 * In Hearthstone, Leokk is one of three possible minions (along with Misha and Huffer) that can be summoned by a Hunter's Animal Companion spell.