Donald Trump got his start to becoming a rich and famous man by working for his father in the area of New York City.  Trump's father was involved in real estate and Trump went to work for him after he got out of college in 1968.

Trump's father was wealthy, but not on the kind of scale that Trump himself is wealthy now.  Trump's father was involved in the retail housing market, building homes and apartment buildings.  Trump had bigger ambitions than that.  He was able to persuade his father to get into buying up real estate in Manhattan.  From there, Trump went on to create huge projects that allowed him to become extremely wealthy.