(New throughout, adds details and after-hours rise in share price)
By Svea Herbst-Bayliss
NEW YORK, Nov 20 (Reuters) - William Ruprecht, the long-serving chief executive of Sotheby's, is stepping down, the centuries-old auction house said on Thursday, roughly a year after activist investors including Daniel Loeb began demanding big changes.
Sotheby's shares rose about 7 percent in after-hours trading, following news of his departure.
Activist investors had called for big changes at Sotheby's including the sale of its headquarters on the upper East Side of Manhattan, and improving its balance sheet.
Ruprecht, 58, started in the rug department and rose to the CEO position where he served for 14 years. The company said he is leaving under a "mutual agreement."
Loeb, who runs hedge fund Third Point, joined the board this year after waging a proxy contest. A year ago, he compared Sotheby's to an "old master painting in desperate need of restoration."
Third Point declined to comment on the move.
Some investors have said privately that they felt Ruprecht had been a barrier to making the auction house more competitive, especially in areas like contemporary art and technology where its rival Christies has made inroads with online auctions.
The announcement was made just days after Sotheby's recorded its biggest auction in history where a sculpture by Alberto Giacometti commanded $101 million. (Reporting By Svea Herbst-Bayliss in New York, and Sai Sachin R in Bangalore; Editing by Sriraj Kalluvila and David Gregorio)