I thought Bill Gates left school to start a company. He hadn't even started a company before dropping out.
(From http://www.microsoft.com/presspass/exec/billg/?tab=biography) While at Harvard, Gates developed a version of the programming language BASIC for the first microcomputer - the MITS Altair.
In his junior year, Gates left Harvard to devote his energies to Microsoft, a company he had begun in 1975 with his childhood friend Paul Allen.