The Classes
The Baldur's Gate manual provides general descriptions of the eight core character classes and eight additional specialty mage classes you can choose from in the game, but here's some additional practical information you should consider when creating your character or choosing among non-player character companions.
Bard
Bards can pick pockets like thief characters, and once they gain an experience level, bards can cast mage spells. Bards can also play an instrument during battle - effectively giving your party members the benefits of a bless spell while the bard continues strumming - and bards can use some weapons not available to thieves. But bards lack the more powerful abilities of thieves, making this "superthief" class less useful than you might initially believe.
Cleric/Druid
Every party must have either a cleric or a druid because of their healing and protective spells. Druids can use daggers and spears, while clerics can't, but clerics are able to wear heavier armor and to turn away or destroy weak undead creatures. Druids are also able to innately transform into animals at higher experience levels. Although clerics and druids both have access to a number of the same spells, there are a number of unique spells for each class. Since the game's manual doesn't set out which priest spells are available for each character class, here's a list of the priest spells that are only available to clerics: command word: die, magical stone, protection from evil, and sanctuary (level one); aid, chant, draw upon holy might, hold person, silence 15 foot radius, and spiritual hammer (level two); and animate dead, dispel magic, glyph of warding, miscast magic, remove curse, remove paralysis, rigid thinking, and strength of one (level three). Here's a list of the priest spells that are only available to druids: charm person or mammal and good berries (level two); call lightning and hold animal (level three); and animal summoning 1 (level four). All other priest spells are available to both classes.