The sentient Wyverns of Kalimdor were eager to ally themselves with the ShamanisticHorde. Impressed by the Orcs' commitment to honor and victory, the Wyverns allowed the Orcs to ride them into combat against those who would disturb the tranquility of Kalimdor and its denizens. The Wyverns, who share a common ancestry with both Dragons and Gryphons, use their powerful talons and razor-like fangs against both airborne attackers and ground troops.
Wind Riders are popular among Orc commanders because they can Bloodlust them for even more damage. Orc players use a combination of Wind Riders and Shamans. It's very important to research upgrades. Wind Riders are especially useful when you surprise the enemy with them and catch them without anti-air defenses.