Commando
The damage-dealing champions of "Final Fantasy XIII," the commando role is designed around physical damage, both for the character set in this role and for the party. The bonus to the party starts at 5 percent for a level 1 commando, growing to 15 percent for a level 5 commando. Additionally, the commando's own damage grows by 50 percent if you fully level the role. Multiple characters with the commando role will automatically stack their party bonus for the benefit of everyone.
Ravager
The ravager is the commando's magical counterpart, offering a variety of elemental-based spells to destroy enemy forces. In addition to magic damage, the ravager fills the chain gauge faster than other roles. The chain gauge is a meter attached to each enemy target that increases every time you attack; as the gauge increases, the enemy takes more and more damage. Leveling your ravager role level not only increases that character's ability to fill the chain gauge, but offers a small bonus to the party's fill speed as well. Much like the commando, two or more ravagers will combine their role bonuses additively.
Sentinel
Every party needs someone to absorb the damage from challenging enemy monsters, and that role is the domain of the sentinel. In addition to drawing the ire of enemies, the sentinel can counterattack when struck and boost his or her innate defense over the course of a long battle. This extra defense carries over into the sentinel's role bonus, which increasingly reduces all damage received by the party as the sentinel gains role levels. Your sentinel characters can gain a personal damage reduction of up to 50 percent at level 5, while subtracting 14 percent damage received from the rest of the party. Though you can add multiple sentinels to increase your defensive bonus, the numbers stack multiplicatively, preventing you from reaching 0 percent damage taken. Instead, you will see sharply diminishing returns from multiple high-level sentinels in the party.
Saboteur and Synergist
The special effects artists of "Final Fantasy XIII" are the saboteur and synergist. Both roles excel at applying powerful status effects to all combantants in the battle; synergists offer "buffs," or positive effects, while saboteurs afflict enemies with negative "debuffs." For example, the synergist can increase the speed of party members while the saboteur decreases the speed of enemies. Saboteur role levels increase the chance of successfully applying debuffs, while a high level synergist gains a large increase to the duration of all party buffs. Both roles function like sentinels when multiple party members of the same type are found; you will get less and less of a return on the bonuses each time you add an additional saboteur or synergist to the party.
Medic
"Final Fantasy XIII's" designated healer is the medic, a support role that also includes resurrecting dead party members. The medic's play style is the simplest in the game, offering only six spells. Your reward for leveling a medic is a sizable increase in hit points recovered from the "Cure," "Cura," "Curasa" and "Curaja" healing spells that make up the bulk of the Medic's arsenal. Like the commando and ravager, assigning more than one high-level medics gives you an additively stacking HP recovery bonus; lots of medics means lots and lots of healing.