Paul Gardner Allen (January 21, 1953 – October 15, 2018) was an American business magnate, investor, software engineer, humanitarian, and philanthropist. Alongside Bill Gates, Allen co-founded Microsoft in 1975, which helped spark the microcomputer revolution and later became the world's largest PC software company. In March 2018, he was estimated to be the 44th-wealthiest person in the world, with an estimated net worth of $21. 7 billion, revised at the time of his death to $20. 3 billion.