Blumenthal a foreign-exchange banker was sent to the United States by
Speyer & Co., and rose to prominence as the head of the U.S branch of
Lazard Frères. He was also a partner of Lazard Frères in France. He retired from Lazard in 1901, giving up his seat on the stock exchange, and returned as a partner in 1906. He returned to the stock exchange in 1916, purchasing a seat for $63,000 (equivalent to $ today). With
J. P. Morgan the elder, he was one of five bankers who saved
Grover Cleveland from giving up
specie payments in 1896, with their $65,000,000 gold loans. where he donated $2 million and where the Blumenthal auditorium is named after him. He was a trustee of the
Metropolitan Museum of Art for many years as well as president of the
American Hospital of Paris. He served as the seventh president of the Metropolitan Museum of Art from 1934 until his death in 1941, where he gave $1 million After his death, he was succeeded by
William Church Osborn. His niece,
Katharine Graham, in her memoir
Personal History, described her uncle as a "difficult man with a big ego". He and Florence also named the Blumenthal Rare Book and Manuscript Library, which contains rare and illustrated books, manuscripts,
Haggadot, as a resource for scholarly research. ==Personal life==