Evoker (Final Fantasy III)

The Evoker (幻術師 Genjutsushi lit. "Illusionist"), also known as Conjurer, is a Job class in Final Fantasy III. It is gained from the Water Crystal. Evokers possess the ability to summon powerful beings into battle. Each possesses a Black and White Magic effect, which is triggered randomly at the time of summoning. For example, the spell Catastro summons Odin. Odin can use Slash (Black), or Protective Light (White).

NES version
The Conjurer is the first Job you get that can summon monsters. However, there is a "White" and "Black" side to each summon. The White side generally benefits the party with a buff or a heal. The Black side generally attacks the enemies. There is a 50 - 50 chance of getting either effect. Once the Summoner Job is available, it is best advised to switch to that one.
 * Special Ability - Summon White and Black

DS version

 * Special Ability - Summon White and Black