Rabten was born to a pair of legendary Earth Kingdom warriors, each carrying a long and bloody resume in service to the Earth King. So obssessed were they with their legacy of warfare, they raised their firstborn son Rabten from the time he could walk to be a living weapon. For years and years, he was drilled endlessly on his parents country estate, living by an incredibly strict rules straight out of basic soldier training.
Rabten hated this life. For one, he wasn't the bloodthirsty type like his parents, and he hated the idea of killing without question for a faraway king. More than that, he hated the inflexible, perfectionist ideals he had grown up with. So, when the opportunity came to leave, when his parents sent him off to the nearest base, he ran from the millitary life and never looked back. So thorough was his rebuke of his parents' legacies, he swore never to touch a weapon of war again.
Unfortunately, he wasn't able to drop all of what his parents gave him. Along with training with weapons such as swords and axes, his parents trained him extensively in hand to combat. With their resources, they were even able to scrounge up an master chi blocking in order to garuntee their son wouldn't just be passed up by some, as they put it, "arrogant rock chucker". As a result, Rabten was still able to handily defend himself from benders and non-benders alike, though he avoided violence whenever he could. His luck rarely afforded him such luxuries, however: danger seemed to follow him like a lovesick puppy. He felt no animosity towards those who attacked him; he felt most people had fairly valid reasons to do what they do (everyone is the hero of their own story), and often conversed with his attackers while they were lying paralyzed on the ground in order to see their point of view and reccomend alternatives.
For years, Rabten wandered about the Earth Kingdom countryside, sipping on peach wine and composing haikus, usually right before being jumped by some punk who just learned enough swordplay or bending to be dangerous. Eventually, he chi blocked in front of the wrong person, a recruiter for a special team commissioned by the Earth King to deal with the growing threat of Chin the Conqueror. He initially refused vehemently, but was soon pressed into service due to his incredibly rare abilities. One does not simply refuse the Earth King's call, after all.