The Thief (シーフ, Shīfu?) is the swift and nimble fighter of the Warriors of Light in the original Final Fantasy, and the secondary melee fighter of the group. He is the game's "investment" character - he initially begins as weak (though buffed in Final Fantasy I & II: Dawn of Souls and subsequent remakes), but after completing the Citadel of Trials, Bahamut the Dragon King upgrades him to the rank of Ninja, and can cast some Black Magic up to level 4. He can use most of the same weapons that the Warrior can, but doesn't have as much variety in armor. He is, however, faster than the Knight, and has a better chance at running away from battle than other classes. In Final Fantasy: Memory of Heroes the official novelization of the game he is a cynic named Sauber.
Unlike most other games of the series, the Thief cannot steal in the original Final Fantasy, but is a valuable asset to the party for his ability to successfully run from battles. He had blue hair in the NES and MSX sprites, but now has a green bandana in the WSC revision and had kept the design, making him resemble Link from the Legend of Zelda.
After the Thief upgrades to Ninja (にんじゃ, Ninja?), he can equip all weapons but the Wizard Staff and Excalibur, all but nine pieces of armor, and can cast low-level Black Magic. In spite of the fact that he has the most drastic upgrade in the entire game, he is still outclassed by a Knight in terms of offense and defense, though later remakes alleviated this to make them more comparable. In all versions, it is recommended to promote the Thief sooner than later, as being upgraded too late runs the risk of decreased spell charges (MP in later editions).
Powers and Stats:
Name: The Thief of Light
Origin: Final Fantasy I
Classification: Human/Hero of Prophecy/The Warrior of Light, Thief/Ninja
Powers and Abilities: Superhuman Physical Characteristics, Master Swordsman, Magic, Elemental Manipulation (Of the ice, fire and thunder variety), Time Manipulation (In the variety of speeding himself/his allies up via Haste and slowing opponents via Slow), Mind Manipulation (Via Sleep), Capable of blinding and stunning his opponents, Can increasing his/allies strength, Can breath underwater (Via Oxyale)
Attack Potency: Large Planet level (Defeated base Gilgamesh in the Lifespring Grotto)
Speed: Sub-Relativistic (Fastest class in the game, and kept pace with Gilgamesh)
Lifting Strength: Superhuman
Striking Strength: Large Planet Class
Durability: Large Planet level (Comparable to Gilgamesh)
Range: Extended melee range with weapons, much higher with magic
Standard Equipment: Katana, Armor, Shield, Crystal, Oxyale
Intelligence: Skilled thief and combatant, bested Garland in mortal combat, previously Cornelia's greatest Knight (Of which was implied to be worth the entirety of Cornelia's remaining military might alone due to the Kingdom's failure to rescue Princess Sara themselves), fairly competent at problem solving with little information available
Weaknesses: None notable
Note: This profile assumes the Thief of Light is the Ninja class from the original game.