S tefan Wirtgen, along with his brother Jürgen, is a German billionaire who inherited the family's massive construction machinery company, the Wirtgen Group. The company was founded by their father, Reinhard Wirtgen, in 1961 as a small hauling business. He later pivoted the company into manufacturing road construction equipment and built it into a global leader in its field. The Wirtgen Group is famous for its road milling machines, which are used to remove the surface of roads, as well as for its portfolio of other road building and mining equipment.

The brothers took over the leadership of the family's business and continued to expand it into a major global player. Their career-defining moment came in 2017 when they sold the family's privately held company to the American agricultural and construction equipment giant, John Deere, for $5.2 billion. This massive all-cash deal was the source of the brothers' multi-billion dollar fortunes. They are no longer involved in the business.