The early Microsoft deal with IBM is the one people study: license the operating system, don't sell it, and keep the right to license it to everyone else. That one clause shaped the whole PC industry.
Microsoft was also very aggressive, and the antitrust case showed how far they were willing to go to crush competitors.
The second career, at the Gates Foundation, is where he's spent most of his time since. Vaccines, polio, malaria. Less exciting to read about, probably more important.