Washington was a surveyor by trade, and was not a rich man. He married Martha Washington, herself the "Teresa Heinz" of her time, who inherited great wealth from her deceased husband who was a very successful planter when he died.
So in short, Washington was the richest President until Trump, by marrying inherited wealth.
-PJ
At the time of his death, Washingtons $780,000 estate was equivalent in value to almost one-fifth of 1 percent0.19 percentof the $411 million GDP. If Washington had lived two centuries later, and boasted a fortune worth 0.19 per cent of the nations approximately $18 trillion 2015 GDP, he would have been worth $34 billion. I’d say that makes him a very rich man!