Paul Gardner Allen (January 21, 1953 – October 15, 2018) was an American business magnate, computer programmer, researcher, investor, and philanthropist. He co-founded Microsoft Corporation with childhood friend Bill Gates in 1975, which helped spark the microcomputer revolution of the 1970s and 1980s. Microsoft became the world's largest personal computer software company. Allen was ranked as the 44th-wealthiest person in the world by Forbes in 2018, with an estimated net worth of $20.3 billion at the time of his death.

Allen left regular work at Microsoft in early 1983 after a Hodgkin lymphoma diagnosis, remaining on its board as vice-chairman. He and his sister, Jody Allen, founded Vulcan Inc. in 1986, a privately held company that managed his business and philanthropic efforts. He had a multi-billion dollar investment portfolio, including technology and media companies, scientific research, real estate holdings, private space flight ventures, and stakes in other sectors. He owned the Seattle Seahawks of the National Football League and the Portland Trail Blazers of the National Basketball Association, and was part-owner of the Seattle Sounders FC of Major League Soccer. In 2000 he resigned from his position on Microsoft's board and assumed the post of senior strategy advisor to the company's management team.

Allen founded the Allen Institutes for Brain Science, Artificial Intelligence, and Cell Science, as well as companies like Stratolaunch Systems and Apex Learning. He gave more than $2 billion to causes such as education, wildlife and environmental conservation, the arts, healthcare, and community services. In 2004, he funded the first crewed private spaceplane with SpaceShipOne. He received numerous awards and honors, and was listed among the Time 100 Most Influential People in the World in 2007 and 2008.

Allen was diagnosed with non-Hodgkin lymphoma in 2009. He died of septic shock related to cancer on October 15, 2018, at the age of 65.