I grew up in a very rich town in NJ and my parents knew a lot of people making more than $5M a year, including some of their close friends. Some examples of their jobs included:
-CEO of a major pharmaceutical company
-CEO of a major investment bank
-Partner in a private equity fund
-Partner at Goldman Sachs (Equity Analysis)
-Fixed Income trader for a major investment bank
-Coach of an NFL team
I'd say the most common routes to that level of income though were private equity and investment banking (particularly traders). I'm sure there were some hedge fund guys too, but I can't think of any off the top of my head. A lot of them were clearly very brilliant, but some of them seemed like they were just in the right place at the right time (i.e. Wall Street in the 80s and 90s)