D uncan MacMillan is a computer scientist and one of the four co-founders of Bloomberg L.P., the global financial data, media, and software company. An expert in computer programming and systems, MacMillan was a key technical mind behind the development of the iconic Bloomberg Terminal, the product that revolutionized the financial information industry.

In 1981, MacMillan, along with Michael Bloomberg, Thomas Secunda, and Charles Zegar, founded the company after they were all laid off from Salomon Brothers. MacMillan played a crucial role in building the robust and high-speed network and data infrastructure that was essential for the Terminal's success, allowing it to deliver real-time financial data to traders and investors. Though he has since retired from an active role, he remains a major shareholder in the highly profitable and privately held company, which is the source of his multi-billion dollar fortune.