Okay, well I'm thinking that his culture of origin would be a nation that lives on a small mountain near a desert, and are capable and sturdy people.
They are a small nation, and therefore do not possess a large warrior base, but train fastidiously and only promote those who show excellent promise and dedication. My character would come from such a background, having been schooled in combat from a young age and trained specifically to be a warrior.
He would not have much knowledge about other parts of the world, barring small wars or skirmishes that he would be involved in in the past. I want him to be about 30, and have a wife and a young child (maybe one to two years old.)
The culture specifically would be one of selective monogamy, but there is no taboo for polygamy or even one woman having multiple husbands. The gender roles therefore are fairly interchangeable, and there is little prejudice between the two. Although, it is understood that women and men excel in different areas, and therefore still tend to focus on different subjects of study.
Due to being persistently on a mountain, the people are not particularly fond of horses or any sort of mount, although respect and often use large animals in combat, just not for riding. Some form of mountain lion or leopard would be bred and trained to be released toward the enemy, dealing terrible damage, and serving as a companion (my character possesses no such companion.)
They are a fairly sedentary culture, preferring to build stable and fortified cities and structures rather than travel from resource to resource. Their reputation for combat prowess precedes them, so they are typically ignored by larger nations, although sometimes bought into alliances with offerings of valuable resources to gain their combat services.
As a society, it is particularly common to appreciate music (like most cultures) but nearly everyone is instructed in a kind of rhythmic chanting, both to assist them in focus and as a form of comfort for children. A different kind of singing, more operatic in nature, is used for entertainment and demonstration. Due to this, they rarely use instruments other than to augment one's voice, or to serve as minor melodic background.
Their religion is one that focuses power within, attempting to understand the great capabilities of the soul and mind of man, and respecting that a man is inherently selfish, violent, and bestial by nature. They attempt to divert this form of energy into one of righteous control, a sort of "cold anger" or complete focus. They utilize this in and out of combat, attempting to seek the fastest, most efficient, and perfect way to accomplish a task.
They are highly skilled masons, and work well with stone. Despite living in the mountains, they are still large of frame, especially in their shoulders, and often use heavy lifting as a form of calisthenics and entertaining athletics.
They are led by a council of three highly respected and highly ordained individuals: one is the current leader of their warrior-monk sect (the group my character belongs to), one is a wise man or woman who has studied the methods of peace and tranquility and brings focus and harmony to the society, and the last one is the interpreter of politics, other nations, and the God Emperor. The third one is a highly respected position, although many feel that they are a form of outsider due to their association with other nations.
They are not a racist or xenophobic people, and in general are gentle but firm. They prefer philosophical conversation over jest, but do have a sense of humor (although it is often seen too tame for some, and too sardonic for others.) They wear heavy clothes, with tighter layers close to their body and progressively looser layers beyond. Their mountain and desert is not especially cold, although in the winter it can snow.
I'd say the overall population, between the several cities spread through the mountain and the desert beneath are, is somewhere in the 500,000 to 1,000,000 range. My character would come from a city upon the mountain, where he owns a fairly nice estate, but is not considered a "noble", although is a rank of some authority within his warrior sect.
That's all I can think of for now, I'll add more later.