Pech

Pech are subterranean humanoids with some Earth-working magical ability, especially in groups. They were introduced in The Lost Caverns of Tsojcanth. They haven't done much in the printed modules; the niche of not-awful Underdark critters was long-established already in the svirfneblin.

They are four foot tall, jaundiced and scrawny, with pupil-less eyes. Pretty much what a D&D-playing nerd grows up as, after his inevitable descent into introversion and alcoholism.

In 2nd edition, they were formally classified as "Elemental Kin", meaning they were residents of the Elemental Planes who weren't the "standard" style mass-of-appropriate-element-given-sentience elemental matter. They were essentially the Plane of Earth's gnome analogue, similar to how Azers were the Plane of Fire's dwarves. Their most unique trait was being so low on the pecking order that they actually frequently left their planar home for the Prime Material because it was safer there.

Forgotten after 2nd edition, Pech were then picked up by Pathfinder; in Golarion, pech are earth elemental fey who were transported to Golarion's Underdark in mass numbers by the Vault Keepers, alien bio-engineers who used them as slave laborers to construct the Hollow World-esque Vaults of Orv. After their masters went into slumber, a number of pech tried to escape to the surface, but exposure to sunlight and subsequently a madness-inducing fungus warped them into the first derro.