A race of cybernetic aliens who are central to the Marathon trilogy of games. The S'pht (pronounce it however you like) were enslaved by the Pfhor over a thousand years before the Marathon game, and are controlled and directed by a single mutant Pfhor aboard each ship. After you destroy that mutant Pfhor, the S'pht are free to assist you (at Durandal's behest) in fighting the remaining Pfhor soldiers.
In Marathon 2: Durandal, you are taken by Durandal to the S'pht homeworld of Lh'owon, where the history of the S'pht race comes to light through a mixture of history and mythology. Lh'owon was colonized by two god-like beings named Yrro and Pthia, fleeing chaotic creatures called the W'rkncacnter. They created the S'pht from the native non-sentient life, but the W'rkncacnter followed. Pthia was killed, Yrro confined the W'rkncacnter to Lh'owon's sun, and the S'pht were divided into eleven clans. The eleventh and most powerful clan was called the S'pht'Kr.
At one point in their history the other ten clans began fighting each other, and the S'pht'Kr abandoned Lh'owon for one of its moons, K'lia. That moon and all on it vanished during the fighting through an advanced "space folding" technology provided by Yrro, to return only when the S'pht clans were reunified. The S'pht'Kr, along with their advanced technology, were gone long before the Pfhor enslaved the rest of the S'pht, but the S'pht left behind a dormant AI capable of contacting them. Eventually, the AI is reactivated, the S'pht'Kr are called back to Lh'owon, and at just about that time all heck breaks loose.
A typical S'pht, also known as a compiler, is much mechanical than organic. It looks like a floating chrome spheroid for a "head", a green energy blaster in the "chest", and a metal "spine" to which those elements are attached. A red or purple cloak covers the spine and blaster until the S'pht attacks, when the cloak is opened and reclosed by a pair of levers at the "shoulders". They can float at any height, and with their cloak appear to be slightly taller than an average man.