Koloss

This is a painted pewter model of a Koloss, which you can purchase at Brandon Sanderson's website.

Koloss are large and dangerous beasts that the Lord Ruler uses in his army.  They are Hemalurgically created, through the use of four hemalurgic spikes stuck through a human body at certain points. While Koloss are regarded as remarkably stupid and reckless, they are not. Koloss are simply unsophisticated, uncultured, and very straightforward. Koloss are also known for being uncontrollable, except by the Lord Ruler. This turns out to be a myth, as they can be controlled by incredibly powerful soothings. Vin is able to control a small army of them using Duralumin during the Siege of Luthadel.

Jastes Lekal is able to command a large army of them by paying them (though using fake money). He marches them towards Luthadel, intending to lay siege to the city. 

No one understands why koloss are willing to work for pay. As it turns out, the Lord Ruler regularly replenished his kososs forces by creating fresh koloss from new hemalurigic spikes. After his death, no one is left to control the kolas. They fight more than usual—leading to exceptionally heavy death rates—but no one provides new spikes. The koloss themselves figure out how to harvest the old spikes from corpses, and to use those spikes to create new koloss. However, hemalurgic spikes leak power when not in use, so they become weaker and weaker through repeated use. Vin is able to figure it out by pushing Human allomantically.

The koloss develop some human characteristics, including a desire for clothes, money and possessions. In at least some cases, they vaguely remember being human.

Koloss continue to grow throughout their life—the older a Koloss, the larger it is. However, the skin doesnt grow with the body. The skin on younger koloss is baggy; on older koloss, it is stretched tight, even torn and ripped.

After the Catacendre

During the remaking of Scadrial, Harmony modified the Koloss. They now reproduce naturally, but at their coming of age, koloss youth must decide whether to accept spikes and become full koloss. Individuals who choose to forgo spikes are known as "koloss blooded". Koloss-blooded humans possess much greater strength and recovery power than a normal human, as well as mottled grayish skin. They can also be allomancers, though it's unclear how common such abilities are among the koloss blooded. For instance, Tarson, one of the Vanishers working under Miles Hundredlives, was a pewter Misting.

Notable Koloss

Full Koloss

• Human

Koloss-Blooded

• Tarson