How to Recruit Regongar
Regongar can be found by freeing him and Octavia at the Technic League Encampment.
A slave of the Technic League along with his lover, Octavia, his magical talents were innate, and honed to dangerous aptitude by his masters. This, along with his unconquerable, violent demeanor, made him a most dangerous slave. After his masters crossed an adventurer, Regongar unexpectedly found himself a free man, eager to use his powers for his own end, for a change.
Regongar is a Magus, which is something of a mix between a warrior and a mage. While not terribly skilled at either one, the synergy between a warrior's melee prowess and an arcane spellcater's buffs aim to close the gap and perhaps provide some extra versatility along the way. As such, you shouldn't play Regongar as just another mage - while he can use his spells to supplement other casters, his Charisma isn't quite comparable to the primary spell-casting attributes of other magically-inclined companions. If you need a Web spell cast, for example, Octavia's will be noticeably more potent.
That said, Regongar can amplify his combat effectiveness with personal buffs like Shield, Mirror Image and Blur. Furthermore, he can wield touch-ranged spells as off-hand attacks, and while this will burn through his spells at a rapid pace, his ability to provide a front-line presence and dish out physical and magical damage shouldn't be underestimated.
He's a bit slow to get off the ground, and for the beginning of the game he'll be a secondary warrior, at best. His spell-buffs will help somewhat, but they're not a great substitute for armor. Once he hits the 7th level, however, and gains access to unrestricted use of medium armor he'll be more well-protected.
His high Strength score offsets a mid-range Base Attack Bonus, and all in all you can expect him to perform about as well as Jaethal in combat, with the caveat that he's more vulnerable in the beginning due to his armor restrictions, and unlike Jaethal he can't wield a shield without incurring the normal arcane spell failure penalties, not to mention the ability to use his off-hand to inflict damage via touch-range spells. Arcane Weapon Enhancement and Arcane Accuracy will further help bolster his melee competence, although they're limited use abilities.
As a fair mix between warrior and mage, Regongar's class skills include Athletics, Knowledge (Arcana), Knowledge (World), Persuasion and Use Magic Device. His good Charisma score makes him a natural at Persuasion.
Early on, Regongar will be a warrior of tertiary quality, capable of dishing out respectable damage, but not being terribly well-protected by Armor Class. Making use of the Shield spell will help, but it's not until the 7th level when he gets access to better armor and more spellbuffs that he'll move to the category of a secondary warrior, fully on par with Jaethal. If you can endure his slow start and relative lack of skill diversity, you'll end up with a versatile - if temperamental - Magus ally.