Yeh'kinya is a level 41 quest giver located at Steamwheedle Port in the contested territory of Tanaris. After  he turns into a green windserpent and flies out over seas. Yelling Blood and souls for Hakkar! HAHAHAH!.
See List of Tanaris NPCs.
He starts the following quests:
After the player completes the quest chain given by Prospector Ironboot, it is revealed that Yeh'kinya is secretly a worshipper of Hakkar the Soulflayer. He has tricked the adventurer into helping him return Hakkar to Azeroth. After the adventurer confronts Yeh'kinya with this knowledge, Yeh'kinya escapes by turning into a wind serpent and taunts his dupe as he flies away. It is then that the player is sent to Yojamba Isle by Ironboot, in order to speak to the Zandalar trolls and discover how to defeat Hakkar. This is a precursor to the Zul'Gurub quests.
CataclysmThis section concerns content exclusive to Cataclysm.
Like most residents of Steamwheedle Port, he has gone missing and possibly killed by the destructive wave that destroyed the port. However, it's possible he left long before the Cataclysm, when he was discovered to be a Hakkar worshipper several years ago.