Dara Mitchell, Sotheby's longtime American painting rainmaker, will retire at the end of the year. She worked for the house for 26 years, first as a senior cataloguer for the American paintings department, and as its director since 1993.

Mitchell's tenure is studded with record sales. Asher B. Durand's Kindred Spirits (1849) was sold in a sealed auction bid for more than $35 million in 2005, making it the most expensive American painting sold at auction at the time. Purchased from the New York Public Library by Wal-Mart heiress Alice Walton, it is now part of the permanent collection at Walton's newly opened Crystal Bridges Museum of American Art in Bentonville, Ark. Mitchell also oversaw the $65.1 million sale of the Rita and Daniel Fraad Collection in 2004, which remains the highest selling total for a single-owner sale of American paintings.

Sotheby's has named Elizabeth Goldberg, currently a specialist in the Impressionist and Modern Art department, as Mitchell's successor. Previously, Goldberg was a senior specialist in the American paintings department.