Steven Anthony Ballmer (; March 24, 1956) is an American businessman and investor who served as the chief executive officer of Microsoft from 2000 to 2014. He is the owner of the Los Angeles Clippers of the National Basketball Association (NBA). As of February 2023, Bloomberg Billionaires Index estimates his personal wealth at around $90 billion, making him the eighth-richest person in the world.

Ballmer was hired by Bill Gates at Microsoft in 1980, and subsequently left the MBA program at Stanford University. He eventually became president in 1998, and replaced Gates as CEO on January 13, 2000. On February 4, 2014, Ballmer retired as CEO and was replaced by Satya Nadella; Ballmer remained on Microsoft's Board of Directors until August 19, 2014, when he left to prepare for teaching a new class.

His tenure and legacy as Microsoft CEO has received mixed reception, with the company tripling sales and doubling profits, but losing its market dominance and missing out on 21st-century technology trends such as the ascendance of smartphones in the form of iPhone and Android.