According to the series bible (pages 23-25), Baltar was originally stated to be from Sagittaron. His parents were not just farmers, but owned a mega-agribusiness setup. One of his earliest memories was his boots getting stuck in cow dung and him having to walk back across the muddy pastures in his socks, arriving back at the house in tears.
His backstory is, essentially, an entire sub-plot, although rather linear and predictable compared to other story arcs in Battlestar Galactica. He quickly distinguished himself in classes and made it through college quickly and had his first doctorate at 21. He also pursued women whenever he had the chance and had to leave one university when he was discovered involved with the wife of a Dean and her daughter after a faculty tea one afternoon.
Since he was born after the war, he, like many in his generation, saw the anti-technology edicts that had come into place due to the Cylon War as foolish and pushed against them, thinking they should be building better technology (that Cylons couldn't crack) than avoiding it.
He also had a massive ego, which was fed by his many sexual conquests as well as his rise in computer work (his passion was computers, his actual field was theoretical physics). He was noticed more and more, was consulted by high ranking government officials, his papers were being read by other scientists (whom he considered as less than himself), and the higher he rised, the more media attention he received and the more women there were for him to conquer. (The series bible compares him to Stephen Hawking, in terms of brilliance and media attention.)
Caprica Six knew what he was like and played him. She was there for him to see and want, but she stayed back because she knew he enjoyed the hunt and when they finally got together, she was aggressive in bed. She let him have his other affairs and didn't ask for commitment. Knowing that he liked the thrill of an illicit affair, she told him she was from a large computer corporation that would be bidding on projects, which would make their affair immoral and likely illegal.
Which brings us up to where we saw Balter at the start of the mini-series: a celebrity, a genius, depended on by the government, and being completely played by Six who knew how to use his ego and lust against him to get the defense codes.
This is essentially a summary of several pages of the series bible. From searching in other areas, most comments that show any awareness of this arc refer back to the series bible, indicating that the bulk of the arc is his backstory, including his hard work, but also his ego and arrogance that led to his downfall. It looks like more elements were going to be added, but that this backstory is the basis for the arc. Other elements would have included racial/ethnic issues, such as how the Sagittarons were treated like second class citizens by the other colonies.