Exarch

Exarch is a draenei title, apparently used for military leaders. The exact context that the draenei use it in is unknown. During the Invasion of Outland period, there was usually only one exarch per zone. On Draenor, there were far fewer Exarchs than there are today - only five at a time - and they were part of the Council of Exarchs.

To become an Exarch, a draenei must go through three trials. They are allowed one companion through their trials. Draenei paladins get an Exarch's Elekk as their mount.

Azeroth

 * Exarch Admetius - Blood Watch
 * Exarch Menelaous - Azure Watch
 * Exarch Larethor - Shattered Sun Staging Area
 * Exarch Thoss - Arathi Basin, Brawl: Comp Stomp

Draenor/Outland

 * High Exarch Commodus - Shattrath (removed)
 * Hataaru
 * Exarch Larohir - Participated in the defense of Shattrath City
 * Exarch Maladaar - Auchenai Crypts
 * Naielle
 * Exarch Nasuun - Shattrath
 * Exarch Onaala - Altar of Sha'tar
 * Exarch Orelis - Area 52
 * Disembodied Exarch - Ruins of Enkaat (multiple, undead)
 * Reanimated Exarch - Auchenai Crypts
 * Exarch Kelios - Deceased

Army of the Light
The Army of the Light has its own Council of Exarchs.
 * High Exarch Turalyon - First non-draenei exarch.

Unknown

 * Exarch Kelios

Warlords of Draenor timeline

 * Exarch Akama - High Vindicator
 * Exarch Hataaru - Chief Artificer (deceased)
 * Exarch Maladaar - Speaker for the Dead
 * Exarch Naielle - Rangari Prime
 * Exarch Othaar - Sha'tari Proconsul (former, became the man'ari Socrethar, deceased)
 * Exarch Phoena
 * Exarch Yrel
 * Exarch Orelis of the Lightbound
 * Exarch Hellscream of the Lightbound
 * When speaking on, Geya'rah speaks of adding another exarch's head to her wall; inferring that she has taken part in the killing of an exarch. It is unknown which exarch she slew.

Notes and trivia

 * Legend tells of Legacy being wielded by draenei exarchs since the time of their banishment from Argus.
 * According to Exarch Onaala, when she was young female exarchs were practically unheard of. Since Exarch Naielle is female, Onaala presumably speaks of a time before she joined the Council.
 * In the Byzantine Empire, the title "Exarch" was used for military governors.

Speculation
There are six active draenei Exarchs in the main timeline. Azeroth and Outland should have no more known than five Exarchs each, discounting the deceased and corrupted. It may be possible that they are on two separate Exarch Councils, one for the neutral draenei and one for the Alliance draenei. It is also possible that the term is used for regional leaders after the collapse of the draenei civilization.