(FORTUNE Magazine) – When Diana Brooks walked into Sotheby's looking for a part-time job while on personal leave from Citibank, she was told nothing was available. That night on the train to Connecticut, Sotheby's chief operating officer happened to sit next to Brooks's boss at Citibank -- who apparently had some pretty nice things to say about his employee. Within 24 hours the 29-year-old lending officer was offered a job working for the U.S. branch of the world's largest auction house. Today Brooks, 37, is president. She is the highest-ranking woman in the land of lots -- and she's barely had to lift a finger. Noted for her financial acumen rather than for her salesroom prowess, Brooks, who is called Dede, has helped restore Sotheby's U.S. branch to profitability by bringing the hammer down on overhead. ''I don't think anyone would describe me as a cream puff,'' she admits. She has also built the company's finance operation into a major profit center. Unlike archrival Christie's, Sotheby's will lend up to 50% of the estimated value of the art that clients want to auction off. Says Michael Ainslie, chief executive of Sotheby's Holdings: ''I've been in business for 20 years and Dede is probably the most effective executive I've ever worked with.'' Brooks has been a key figure in staging two highly publicized upcoming auctions: the $2 million estate of Clare Boothe Luce, and Andy Warhol's estate, worth an estimated $15 million. The ten-day auction in April of Warhol's personal collection of 10,000 items will be the largest ever held on Sotheby's premises, and should net the company more than $1 million.