Inquisitors have become a favorite in many fantasy settings as they combine good reasons to travel and hunt down others although with enough grimness to their characters to make them interesting and give them intriguing backstories.
Historically, inquisitors were created by the Roman Catholic Church around the start of the 12th century to seek out those who erred away from the Christian faith and to punish them for their blasphemy. At the time, their major target would have been Cathars. They used a court process based on Roman law, and worked within this judicial system of the church. When someone was found guilty of unrepentant heresy, the guilty party was required by law to be handed over to secular authorities for final sentencing and punishment. Punishments included life imprisonment, banishment, and the ever popular burnt at the stake until dead. Lighter sentences also existed, like fines, having to recite prayers, do a pilgrimage or house arrest.
They are typically portrayed in fiction as having a tendency to love screaming 'It's a witch!' and trying to burn people at the stake, believing if it was a witch they would save themselves with their magic and prove their crimes and if the person was innocent... they would prove their innocence by burning alive. In actuality the Catholic Church - and their inquisitors - didn't much care about witches. They were MUCH more concerned with Jewish and Muslim peoples, or whoever else was unpopular at the time.
Inquisitors have come into popularity in recent times, as the rise of gritty realism means the idea of relentless hunters of the faith and all the grimdark that goes with it is attractive. There are also near limitless possible stories to use them in. Look at GW for example; the Inquisitors and Inquisition of their setting has become such an integral part of 40k it is hard to imagine it without them.
An Inquisitor is an agent to a particular deity who police enemies of their faith, seeking them out using guile and cunning and often bending the rules of their faith in doing so. This they have few qualms about doing, seeing themselves as loyal only to their deity and their own brand of justice, and using their actions as proof of their devotion. Between their casting, high skills and class features, Inquisitors are tier 3: able to do a variety of things well enough, though their abilities don't synergize that well and their spell list is the worst of their lot, means it takes some char-op to find a way to make them synergize well enough to be a specialist in something.
They cast divine spells and get the same spell progression/skill point as a Bard, but bear no other resemblance to that class. They use a combination of divine spellcasting, special curses, and the ability to make their weapons have the Bane property against their current opponent to fuck shit up as much as possible. Also they can choose either a Cleric Domain, but without bonus spells, or an "inquisition" which grants them all kind of tricks ranging from proficiency with firearms and the ability to blow up wizards concentration (other than their squishy heads) by shooting'em, to run like a monk, heal themselves as a paladin, and rage hard as a barbarian, making Commissar Fuklaw proud of them.
Because of the need to find and destroy the enemies of their faith, Inquisitors need to travel and to be a member of a party even if just to disguise their presence. Their fellows should beware though as even they are not above suspicion (and may get a knife in the back if not careful in their words...)
Oh, and Horror Adventures has the Living Grimoire archetype, which gets to beat his enemies to death with a giant holy book. That is all you need to know.
|The Classes of Pathfinder 1st Edition|
|Core Classes:||Barbarian - Bard - Cleric - Druid - Fighter - Monk |
Paladin - Ranger - Rogue - Sorcerer - Wizard
|Alchemist - Antipaladin - Cavalier |
Inquisitor - Oracle - Summoner - Witch
|Arcanist - Bloodrager - Brawler - Hunter - Investigator |
Shaman - Skald - Slayer - Swashbuckler - Warpriest
|Kineticist - Medium - Mesmerist |
Occultist - Psychic - Spiritualist
|Ultimate X:||Gunslinger - Magus - Ninja - Samurai - Shifter - Vigilante|