There are three different tiers of Character Class. All characters begin at level 1 in the first tier as the Mortal Class, and are limited to learning Mortal Skills.
When the character earns enough experience to become level 10, they are able to choose a second class from the Tier 2 classes. There are currently 6 different tier 2 classes to choose from (two of each Alignment, though the choice is restricted based on the character's Morality.
When the character earns enough experience to become level 20, they are able to choose a third and final class from amongst the tier 3 classes. This choice is restricted based on the tier 2 class of the character.
All characters are able to purchase skills from all of their character classes, i.e. an Infernal Behemoth (tier 3) can still purchase skills from the Pariah (tier 2) and Mortal (tier 1) class skills.
Tier 1: Mortal
Good Combat Classes
Good Spellcaster Classes
Neutral Combat Classes
Neutral Spellcaster Classes
Evil Combat Classes
Evil Spellcaster Classes