Robert Deniro: This actor left high school before his 17th birthday. The two-time Oscar winner studied his craft at Lee Strasberg's Actor's Studio and the Stella Adler Conservatory. De Niro learned a thing or two about business along the way, too: His financial portfolio includes film studio TriBeCa Productions and a handful of posh New York eateries.
Catherine Zeta Jones: The daughter of a seamstress and factory owner quit school at age 15 to pursue a stage career in London. The smoldering Welsh actress rose to fame in the late '90s with her performance alongside Anthony Hopkins and Antonio Banderas in The Mask of Zorro.
Simon Cowell: The caustic judge pulled down an estimated $80 million last year, thanks to his involvement withAmerican Idol;Britain's Got Talent; musical talent show The X Factor; and SyCo records, his production company. The 50-year-old impresario dropped out of school at age 16 and landed a job in the mail room at EMI.