Dan Loeb is adding art criticism to his investor activism, accusing the management of auction powerhouse Sotheby's of failing to understand what kind of art sells best.

The hedge fund manager is seeking to oust William Ruprecht as the chairman and chief executive officer of Sotheby's, claiming the auction house's leader has failed to grasp the modern art world. Instead, Loeb, himself an avid art collector, says he should be on the board.