did not start his own, he renamed the existing family business Elizabeth Trump & Son when he became President of it.
https://en.wikipedia.org/wiki/Donald_Trump 'Real estate
The distinctive façade of Trump Tower, the headquarters of The Trump Organization, in Midtown Manhattan
In 1968, Trump began his career at his father's real estate development company, Elizabeth Trump & Son, which owned middle-class rental housing in New York City's outer boroughs, but also had business elsewhere.[90][91] During his undergraduate study, Trump joined his father Fred in revitalizing the foreclosed Swifton Village apartment complex in Cincinnati, Ohio, boosting the occupancy rate from 66% to 100%.[92][93]
When his father became chairman of the board in 1971, Trump was promoted to president of the company and renamed it The Trump Organization.[6][94] In 1973, he and his father drew wider attention when the Justice Department contended that the organization systematically discriminated against African Americans who wished to rent apartments. The Department alleged that the Trump Organization had screened out people based on race and not low income, as the Trumps had stated. Under an agreement reached in 1975, the Trumps made no admission of wrongdoing and made the Urban League an intermediary for qualified minority applicants.[95][96] His adviser and attorney during (and after) that period was Roy Cohn, who responded to attacks by counterattacking with maximum force, who valued both positive and negative publicity, and who Trump emulated.[97]'
His Dad also gave him millions to start with.
Trump 2000?
https://news.artnet.com/app/news-upload/2016/11/trump2000.jpg