Kurogane's parents Gopan and Jaya were once wealthy Earth Republic nobles who lives illustrious lives in the Upper Ring of Ba Sing Se, who were also known as some of the most vain and petty people the Upper Ring has ever housed. However this pettiness eventually cost them their lifestyles when another noble family mentioned their notoriety as vain and selfish people. Angered beyond the point of reason, Gopan and Jaya invited many nobles over for a gala and attempted to poison every single one of their guests. However their plan was found out and they were quickly exiled to the Lower Ring and stripped of all their privileges. Soon afterward they had their son Kurogane.
Despite their best attempts to make Kurogane into a worthy noble heir, he was willful and often ran off to play with the children of the slums rather than learn the customs of the nobles. After a few years of this his parents gave up on trying to make him a proper heir, rather they decided to use him to take revenge on the nobles that had exiled them by using Kurogane's earthbending. His father began teaching his son how to attack and destroy anything and everything with his earthbending once he turned ten, hoping to toughen him up for when he would kill the nobles. Though Kurogane preferred to create with his powers over time he began to enjoy the destructive nature of his father's teachings as well, to the point where he stopped using earthbending around his friends in fear of accidentally killing them.
A few months after completing his training, Kurogane's parents learned of a noble visiting the Lower Ring to intermingle with the commoners and decided that this would be the best chance for Kurogane to begin his career as a slayer of Earth Republic nobles. However the noble fought back, and Kurogane was hesitant to kill him. Between his parents calling for the noble's blood and his friends and the injured noble begging him not to kill Kurogane...snapped. By the time he had come to his senses he had killed the noble, his parents, his childhood friends, and almost fifty other innocent bystanders with his earthbending. Horrified, Kurogane fled the city and ended up in the Si Wong Desert.
In the sands of the great desert Kurogane was determined to die, and once he was sufficiently lost and overheated he happily succumbed to the intense heat. Fate had other plans, however; an old sandbender found him passed out in the sand and took him back to his lonely abode to heal. When awoken Kurogane was angry he was saved, but the old man suggested letting him become his assistant rather than waste away in the burning sands. Believing there was no where else to go, Kurogane accepted and became the old sandbender's assistant. He helped fight off bandits, gather food and water, and even build a sand sailor for them to travel with. While helping around Kurogane and the old sandbender talked about philosophy, with the old man believing in preserving the balance of the world. He spoke of how everything and everyone is part of one great being, and if we try to destroy each other it would only end up causing a catastrophe of apocalyptic proportions. Kurogane listened intently, and over the two or three years as the old man's apprentice became determined to help keep the world in balance no matter what.
When he told the old sandbender of his new objective in life, the old man was overjoyed that his assistant had taken his words to heart. He suggested they go to Republic City, where between the Rebellion and constant in-fighting had been thrown out of balance for a very long time, and Kurogane eagerly agreed. However they were beset by a large group of bandits just outside the desert looking for revenge. The old sandbender took them all out, but before he could finish them off he was killed by Kurogane. In his mind, the old sandbender was disturbing the worldly balance by defeating all his foes rather than simply leaving them to fight again and Kurogane was forced to intervene. He then killed the bandits, as they were equal in power to the old sandbender and so it "set the scales right again", before leaving. He travelled throughout the Earth Republic, maintaining the balance he so fervently protected, and after a year he finally made it to Republic City. He was ready to bring back balance to the city in any way possible.