The Investigator is a Pathfinder Class found in the Advanced Class Guide. It combines together the casting abilities of the Alchemist with the skillmonkeying of the Rogue, and manages to outdo both parent classes in support and skillmonkey roles though at a cost of combat ability.
As an alchemist, nothing changes mechanically with how many spells can be cast. However, the Investigator loses out any chances to use bombs, with Mutagens only being given as Discoveries and potions being Feat-only. The investigator gains his talents at the same rate the alchemist gains discoveries, but a level slower. As a Rogue, the Investigator actually gets 1 more skill rank than standard and get a good lot of the skills available between both classes, and with invisibility as level 2 Extract, Stealth as class skill, trapfinding, inspiration to both sneak and perception as well as dependency on Dex, the investigator outdoes the rogue as a party scout by miles upon miles. That said, however, Investigators do get access to both Alchemist Discoveries and Rogue Talents in addition to their own unique Talents which add to their capabilities as a utility knife.
What they gain as a unique feature is "Inspiration", which is a limited number of boosts that can be spent to boost up a test by d6(1d8 with Amazing Inspiration talent at level 7 (upgrades to 2d8 at level 20), also the inspiration die can be rerolled with Tenacious Inspiration at Level 13) each day, with using it in combat costing double (Combat Inspiration reduces the costs) and being free on Knowledge, Spellcraft, or Linguistics if the skill's trained (But it can also apply to a myriad of other skills like diplomacy, disable device etc with talents like "Underworld inspiration"). As they level up, the pool of free uses and the limit of how many they can use per day grows, granting them more utility, and they also gain an ability to study a target to add extra effects to their attacks and maneuvers (like making his targets automatically sickened or blind without giving them a saving throw). Studying a target grants the investigator half of his level on attack and damage rolls that lasts up to his Intelligence mod in rounds, and the duration can be doubled with the proper talents. In any case, Investigators are best utilized as a support-type with mixed utility in mundane and alchemical applications. In a more social game, however, they become even more useful with the proper talents giving them free inspiration rolls anywhere they want.
Archetypes can tinker with the skillmonkeying even more, with sorts like the Empiricist weaning off a high dependence on Wis and literally rejecting illusions, the Sleuth replacing Alchemy with Luck from to be spent like a Gunslinger's Grit (Speaking of, there's also an archetype that makes your Investigator a Gunslinger-lite, Grit and all), and the Mastermind going more social earlier and providing Inspiration to an ally. New Scavanger archetype turns you into the engineer from TF2, so go wild. Tl;dr: Investigators are rogues if rogues were tier 3 instead of being tier 6.
|The Classes of Pathfinder|
|Core Classes:|| Barbarian - Bard - Cleric - Druid - Fighter - Monk |
Paladin - Ranger - Rogue - Sorcerer - Wizard
| Arcanist - Bloodrager - Brawler - Hunter - Investigator |
Shaman - Skald - Slayer - Swashbuckler - Warpriest
| Alchemist - Antipaladin - Cavalier |
Inquisitor - Oracle - Summoner - Witch
| Kineticist - Medium - Mesmerist |
Occultist - Psychic - Spiritualist
|Ultimate X:||Gunslinger - Magus - Ninja - Samurai - Shifter - Vigilante|
| Aegis - Cryptic - Dread - Marksman - Psion |
Psychic Warrior - Soulknife - Tactician - Vitalist - Wilder
|Path of War:||Harbinger - Mystic - Stalker - Warder - Warlord - Zealot|