There are a total of 12 jobs in Final Fantasy 1. Each of them has its own strength and weakness. Having a balance party that consists of various jobs within your party is recommended.
Job
Description
Warrior
Naturally has high strength and defense, but can't use magics.
White Mage
Capable of using low to mid-level white magic spells.
Black Mage
Capable of using low to mid-level black magic spells.
Red Mage
A well balanced fighter and magician. Can most of the common
black & white spells. Also has decent attack power.
Monk
A really stong fighter, especially without any weapons
equipped.
Thief
Most useless class. Has weak strength & defense, but good at
feeing from battles.
Knight
Upgrade for the warrior class. Powerful fighter, and allowed
to use white magics of up to level 3.
White Wizard
Upgrade for the white mage class. Can use better equipments
and high level white magics.
Black Wizard
Upgrade for the black mage class. Can use better equipments
and high level black magics.
Red Wizard
Upgrade for the red mage class. Can use better equipments
and certain black & white magics of up to level 6 only.
Master
Upgrade for the monk class.
Ninja
Upgrade for the Thief class. Can use better equipments and
a decent fighter. Can use black magics of up to level 4.