Agent 13 is an independent operative fighting the Brotherhood.
Millenia ago the advanced civilization of Lemuria thrived and for centuries seemed unbeatable. Then barbarian hordes increased their thrusts into that empire's lands and gradually destroyed it. The few survivors managed to create a secret base where they were able to preserve their technology and their culture.
Over the many centuries that saw the slow advance to these days, the hidden descendants of Lemuria watched and often manipulated the goings of the outside world. Many events throughout history that looked odd and unexplanable were the results of Lemurian intervention, all extremly covert.
With the turn of the 20th century, the leadership of this group grew less inclined to stay in the shadows and more determined to resume their rightful place as rulers of the world. The primary leader, a person known as Itsu but also as the Hand Sinister, has molded the organization into a group calling itself the Brotherhood and dedicated to world dominations.
In 1907, a very young boy, showing great signs of tremendous ability and potential, was kidnapped from his home and taken to the Brotherhood's headquarters, the Shrine. There he was given the designation of Agent 13 and trained to become one of the elite operatives for the Brotherhood, a man skilled in assassination and able to handle all manners of covert missions. His ability to learn and improve on his training was incredible and before long he was their best agent.
Being as good as he was, though, it was almost inevitable that this man capable of learning all sorts of secret information would learn of the Brotherhood's real plans of taking control of all government and subjugating the people. He rebeled and was thus branded a traitor and marked for death.
He did not go easily into the final sleep, though, and he mounted his own war against his former teachers. He quickly showed them that they had taught him well. He put together his own small but effective team as dedicated to bringing down the Brotherhood as he was and with his new friends, his ability to harass the Brotherhood became legendary, making him their greatest enemy.