This is a brief list of the types of characters that can exist on Argilla.  New adventurers can be almost any of these.  Which class they can be depends on the characteristics the new adventurer has.

Characteristics are determined by creating eight attribute scores.  Four of these represent physical characteristics while the other four represent mental one.
Strength - Physical strength.
Magery - The ability to use magic.
Theurgy - How well you can deal with the gods and holy items.
Constitution - Overall physical conditioning.
Dexterity - Upper body movement and positioning.
Agility - Lower body movement and overall body positioning
Perception - The ability to notice things going on around you.
Ego - The power of the mind.

Alchemist
Alchemists play with various materials to produce potions or other items that have different uses.  Some of the more famous substances include Foam Stone, Healing Potions, and Iron Bones Potions.

Beast Master
A form of cleric that worship the Beast Lords.  Commonly seen with familiars of many different forms.  There are lots of jokes made about elven Beast Masters.

Cleric
A priest to one or more of the gods.  Clerics will normally begin with a small set of ceremonies and the Book of Common Prayers for their god.  Weapons restrictions vary by god, usually more by custom than by law.  In some cases, the clerics will be noncombatants (Kiralt).  Clerics are allowed a set amount of power from their god that they can use on a daily basis, provided they are devout and perform their daily rituals.  Clerics with the right ceremony, and enough mana, can even restore people to life, given they haven't been dead too long.

Dragon Lord
Another form of cleric.  These draw their power from the Ancestral Dragons.

Fighter
The Grunts, these guys are the specialists with weapons.  They have no ability to cast spells, get their prayers answered, or use the power of their mind on a regular basis.  The fighters are usually the best people using conventional weapons.

Hero
This is a slightly different type, most heroes are fighters, but some may be mages or thieves.  The distinguishing feature of heroes is their Luck.  Most heroes worship Random, after all, heroes are allowed to be lucky.

Mage
The mage can manipulate mana using the language of magic.  Given enough time they can do almost anything, but have a limited amount of spells that can be cast while in combat (quickly).  Mages can make temporary or permanent magical items.

Martial Artist
Fighters who specialize in mainly unarmed combat.  They rarely wear any form of armor, and often fight without weapons of any type.

Necromancers
Not often seen, these people play with dead bodies.  They are tolerated only because they are the only ones who can repair dead bodies so they can be restored to life.

Paladin
The holy fighters who protect the followers of the god.  Paladins can be of almost any class, but are rarely clerics.  They are given special abilities by their gods, usually after performing some deed for that god.

Psychic
These people use the power of their minds to affect other people or things.  Psychics can read minds or heal people, in some cases they can make talismans that allow non-psychics to use psychic abilities.

Thief
Your classic sneaky people.  Specializing in sneaking, picking pockets, disarming traps, and opening locks.  Not all thieves steal things, but many do.  Some thieves prefer to be called scouts by other people.

Combination
4th Age allows anyone with the appropriate attributes to be any and all classes they qualify for.  This has the advantage of more abilities for the characters but it also means more things to improve which results in slower overall improvement.