Thieves have high speed and agility but average attack power and defense power. They have the ability to steal items at the end of a fight. In addition, they are decent combatants that can use whips and chains to attack multiple enemies at once. In the outside world abilities such as Eagle Eye allow the player to locate villages and nearby towns.
The Thief's best skill is Smell which allows treasure hunters to know how much treasure is left on a particular floor. As for hybrid skills, Thief Hit, the hybrid skill of a Warrior and a Thief, is probably one of the useful hybrid skills to learn as it has the chance of taking one item from a monster regardless of whether or not it is defeated. However, the stealing rate is quite low. To this end, the character must have a high luck value to steal successfully.
Regarding evolution, the Thief can combine a mastered Shepherd class to become a Tamer. They will learn all sorts of breath skills and have a chance at taming monsters for the Monster Park. The Thief can also combine a mastered Mariner class to become a Pirate. The Pirate learns sea based attacks which is useful as most monsters, save the aquatic ones, don't have resistance to these skills. Plus they are cost effective.
The Thief vocation is available at the start of the game (start of game meaning when you have access to "Patty's Party Planning Place") and has the unique skillset "Acquisitiveness". Thieves can also use skill points to learn Sword, Knife, Claw, and Fisticuffs skills. Their Coup-de-Grace is "Itemized Kill," which guarantees treasure dropped after the battle (some say this is a better method of item farming than using the "Haulellujah" (Co-op De Grace}).