Trump had a half-century career and a highly highly successful real estate mogul and businessman. You don't get to be a billionaire if you aren't successful.
You don't know how he made his money and if was all legal, he would have made much more. He was sued for his Trump University scam. Trump has a long record of bankruptcies, lawsuits (over 5000), and business failures, but also several wins in branding himself and the Trump name across several platforms such as The Apprentice. Donald was 'earning' $300k a year since the age of three and was a millionaire by the time he was eight years old. Was that because he was a good businessman? When he got older, his father Fred gave him control of apartment buildings in Queens. It was at his father's real estate company that Trump got his start in business. In 1971, he took control of his father's apartment rental company, Elizabeth Trump & Son Co., and later on, he renamed it The Trump Organization.
In the early 1990s, Trump’s winning streak ground to a halt. The national economy started to slow down, and New York's economy stalled, causing Trump’s income streams to dwindle. Soon, he found it difficult to make the interest payments on the debt he'd accrued to finance his different businesses. His annual loan payments were $300 million. The Trump Organization and its subsidiaries owed $9 billion and Trump's personal debt totaled $975 million.
To avoid having to file for bankruptcy, Trump met with four of his major lenders, Citibank, Bankers Trust, Chase Manhattan Bank, and Manufacturers Hanover Trust Co.—now owned by JPMorgan Chase Bank, National Association. The banks were concerned that if they foreclosed on his properties they, too, would lose tremendous amounts of money.
In the end, Trump convinced the banks to loan him an additional $65 million, which he'd use to keep his businesses afloat. The banks also agreed to defer, for five years, the interest and principal payments on Trump's outstanding loans. (don't we all wish our banks would do that for us?) Some of Trump's debts were paid down with funds from the sale of his assets, which included an airline company (Trump Shuttle) and a yacht (which was sold to Saudi billionaire Prince Al-Waleed bin Talal). Trump also sold his controlling stake in the Plaza Hotel and turned his Florida beach house, Mar-a-Largo, into a resort.
Trump has been great at several things including cheating on his income tax. Pushing his name brand and selling it to display on other people's buildings was a success. The Apprentice was wildly successful for people who had no idea who or what Trump was. His 3 casinos were dismal failures. His airline, the Trump Shuttle and his football league, United States Football League failed. His Trump Steaks failed. His Trump University failed. And until we get to see his income tax returns for the past 8 years, nobody knows for sure how successful he really is.