Darahir

Darahir can be found at The Black Market in the Underbelly of Dalaran.

He sells a companion in unlimited supply.

Looking closely at his face, he uses the NPC skin found on Dar'Khan Drathir.

Speculation
It is commonly believed that he is, infact, a former Darkfallen. It is noted that all Northrend NPC's using the same skin are darkfallen.

It is also possible that he is a deceased former occupant of Dalaran, who resides now in the Underbelly. Possibly, he is shunned for his use of dark magic or even necromancy, as he sells floating skulls, and is dressed in robes that suggest his unusual profession; the Dreadmist Raiment.

Judging by his voice files, he apears to have been a high elf in life. The same voice files are shared with high elf NPCs, and also the male counterpart of the current Dark Ranger's voice used in World of Warcraft: Wrath of the Lich King, which is an edited version of the night elf NPC voice.