Human is a very special koloss. He's quite a bit older than most, his creation running all the way back to before the Lord Ruler's death. He was originally the leader of a rebellion out in the southeast—the same area where Clubs spent his youth fighting. Human, then known as Vershad, was one of the more successful leaders of the wasted men—those who live out in the desert outside the borders of the Final Empire, but come in to raid and steal supplies from outlying villages.
Charismatic and intelligent, he managed to keep his band alive even once the Lord Ruler turned his attention on them. Rather than ravaging villages, Vershad would convert them—quietly, carefully—to his side and get them to give him supplies. In turn, he would "raid" them and destroy the lords' mansions, causing chaos and letting the people get a sideways revenge against their masters. In the chaos, it would be assumed that the raiders got away with the skaa food, and it would be replenished.
The Lord Ruler tired of such games and eventually sent his koloss against Vershad and his men. As clever as they were, they weren't able to stand against a well-laid betrayal and ambush set by an Inquisitor—one who controlled a troop of koloss. The raiders were slaughtered, and Vershad himself was turned into a koloss for his crimes.
He retained enough of his determination and his intelligence, however, to make a remarkably clever koloss. (There is some variety to koloss, based on who they were before the transformation.)