Elizabeth Holmes

In a June Fortune cover story, 30-year-old Elizabeth Holmes finally lifted the veil on the secretive, disruptive blood-analytics company she founded in 2003 when she was just 19. The rapidly expanding firm, Theranos, can perform hundreds of diagnostic tests using just a few drops of blood painlessly drawn from a pricked finger—while charging just a quarter to a tenth of what the incumbents do. Holmes still owns over half the stock in Theranos, which investors value at more than $9 billion and which now employs more than 700 people. —Roger Parloff