As head of Wal-Mart's warehouse club business, Brewer runs one of three operating segments at the retail giant. With $56.4 billion in revenue, it's so big that it would rank No. 53 on the Fortune 500 if it were a standalone company. The Lockheed board member drove sales up 5%, and operating income up 6% at Sam's Club and has been building its online business. She also has the ear of CEO Mike Duke: Brewer is his direct report, and the two have one-on-one sessions at least twice a month.