The koloss were a bestial race of creatures on Scadrial, featured in the Mistborn trilogy, created by the Lord Ruler through the use of Hemalurgy. During the time of the Lord Ruler, koloss served as a powerful, fiercely loyal army to him, thanks in no small part to the fact that they could be controlled through the use of Allomancy by any powerful Mistborn or group of brass mistings. . After Harmony's Ascension, however, the koloss were transformed into a tribal race that could breed, which lived in the Roughs. 
When a fellow koloss dies, other koloss in the vicinity would attempt to collect and reuse the spikes from the dead one. This resulted in the koloss being able to reproduce in a manner of speaking, provided that they had someone to stick the spikes into. The koloss were periodically supplied with fresh spikes and skaa captives to produce more koloss, but after the death of the Lord Ruler, they learned how to reproduce on their own, via harvesting the spikes from their dead brethren and re-using them.
Because of this, after the Lord Ruler's control over the koloss ended, many of the koloss would attack nearby human inhabitants.
The koloss were physically very large and very powerful. A full sized koloss could grow to be as tall as twelve feet. A young koloss had as much skin as it would come to have in its later life. Because of this, the younger a koloss was, the fatter they looked due to having too much baggy skin covering themselves. The skin itself didn't hold terribly firmly to the koloss' body. When a koloss reached about twelve feet, their hearts could no longer sustain their bodies, and they would die shortly thereafter.
Similar to Steel Inquisitors, the creation of a koloss was very brutal. To create a koloss, 4 humans were stabbed with individual iron spikes through their heart, and these spikes were then placed strategically on to a fifth person, causing them to becomes a koloss. These spikes could be reused, however, the power of the spikes decreases with re-use.
The only real powers in a koloss' arsenal were superhuman strength, and increased size. However, this came at a price. Koloss in the Final Empire were nowhere near as intelligent as they were as a human. However, they still retained the faint ability to reason, and the ability to communicate, and the re-use of spikes from dead koloss to create more resulted in koloss that retained more of their former humanity.
Because of their diminished intelligence, the Final Empire-era koloss lived in barbaric tribes. Usually, social standing was determined by age, because as the koloss ages, they got larger and more powerful.
Koloss were said to have two emotional states: boredom and rage. Because of this, their day to day lives were filled with milling about and fighting. When there was nothing else to fight near them, the koloss would turn to in-fighting.
Most of the killing within a tribe was done solely on a whim, usually to get something the other koloss owned, or because some random glance or act had enraged one of the koloss.
After Harmony's Ascension, koloss were physically changed to become a true breeding race. Not much is known about koloss culture during this era of Scadrial as of yet, but it can be assumed that their culture must have changed in some way as a result.
 Notable Koloss
|The Metallic Arts|
|Arts||Allomancy · Feruchemy · Hemalurgy|
|Concepts||Metalborn · Snapping · Savants · Metalminds · Twinborn · Compounding · Blessings|
|Constructs||Steel Inquisitors · Koloss · Kandra|
|Base Metals||Iron · Steel · Tin · Pewter · Zinc · Brass · Copper · Bronze · Cadmium · Bendalloy · Gold · Electrum · Chromium · Nicrosil · Aluminum · Duralumin|
|God Metals||Atium · Malatium · Lerasium|
|Mistborn Series (Scadrial)|
|Books||First Mistborn Trilogy (Mistborn: The Final Empire, The Well of Ascension, The Hero of Ages) · Mistborn Adventures (The Alloy of Law)|
|Shards||Preservation · Ruin · Harmony*|
|Races and Creatures||Skaa · Nobles · Terrismen · Inquisitors · Koloss · Kandra · Mistwraiths · Southern Peoples of Scadrial|
|Magic||Metallic Arts (Allomancy, Feruchemy, Hemalurgy) · Metalborn · Mistborn · Misting · Savant · Ferring · Twinborn · Compounding · Atium · Lerasium|
|Other Media||Mistborn Adventure Game · The Eleventh Metal · A House of Ashes · Mistborn: Birthright · Mistborn film|