Ad budget: $600 million globally
Agency: Ogilvy & Mather Worldwide
Career: Joined American Express in 1979 and moved up the marketing ranks. Was also exec assistant to then-AmEx President Louis V. Gerstner Jr., 1986-'87. Was a senior VP there in 1993 when she was recruited to IBM by its new chairman-CEO, Mr. Gerstner. One year later, Ms. Kohnstamm fired more than 80 agencies and consolidated at Ogilvy in the biggest account shift in history.