Dark Mage

The Dark Mage is a class that appears in Fire Emblem: Monshō no Nazo, Fire Emblem: Seisen no Keifu, Fire Emblem: Thracia 776, Fire Emblem: Shadow Dragon, Fire Emblem: Shin Monshō no Nazo ~Hikari to Kage no Eiyū~, and Fire Emblem: Kakusei. The Dark Mage's equivalent in the Game Boy Advance Fire Emblem games is the Shaman. In Thracia 776 it was a promoted unit that promoted from Lopto Mage.

Fire Emblem: Shadow Dragon
In Shadow Dragon, Dark Mages actually have less magic than Mages (During class change a none magical unit going to a Dark Mage will only gain +2 while Mages gain +3) Though they generally have higher defense.

Also, it may be noted that there are no magic types in Fire Emblem: Shadow Dragon. Therefore, Dark Mages can use any given Tome (with the adequate spell level) whereas Shamans can only use Dark Tomes.

If you seek to reclass a unit into a Dark Mage, Cord and Caesar are recommended, as they both have a 30% growth rate in magic as dark mages.

Monshō no Nazo

 * Gharnef: The Dark Pontifex who wishes to revive Medeus and destroy the world.

Seisen no Keifu

 * Sandima: Member of the Lopto Sect who manipulated the country of Verdane.

Kakusei

 * Sariya: A mage from Perezia who doesn't care about the war between Perezia and Iris
 * Henry: A mage from Perezia who loves war and joins the Iris army solely to be able to fight more.