From Unofficial Ansalon Wiki
Thieves are a good class, those who think otherwise have never perfected playing the class. They do a few things better than any other class, but have the widest range of skills available. Thieves are specialists at thievery and covert actions, being capable of entering areas undetected where more powerful adventurers would fear to tread. They are better fighters than clerics, but lack the wide weapon selection of warriors. Their backstab is dreaded by any who fall under their knives.
All thieves begin with the dagger combat skill, and are learned in steal as well. Any other weapon skills must be purchased, unless the default selection is chosen.