Aby J. Rosen (born 1960) is a German-born real estate tycoon living in New York. He is the co-founder of RFR Holding, which owns the Seagram Building and Lever House, among other properties. Rosen is also a noted collector of modern and contemporary art.

Early life and career
He was born in Frankfurt, Germany in 1960. The son of Jewish Holocaust survivors. His mother Anni spent World War II hiding in a Belgian farmhouse while his father Isak was interned in concentration camps in Germany and Poland. After the war, his mother became a painter and his father a real estate developer.
In 1987, he moved to New York City where he apprenticed at a real estate brokerage firm selling properties to German investors.

Real Estate Holdings
In 1991, he founded the partnership RFR Holding LLC with his childhood friend Michael Fuchs (who was also the son of Holocaust survivors). Although the real estate market was in a downturn at the time, they had access to capital initially using properties they each owned in Germany as collateral and later, leveraging their access to German investors. Their strategy was to purchase large, vacant office buildings in need of an upgrade and then hiring the best architects to refurbish them to exceptional standards. In the 15 years after RFR Holding was established in 1991, Rosen had acquired a vast portfolio of real estate holdings including the landmark Seagram Building and Lever House.

Noteworthy Developments
Gramercy Park Hotel
Rosen partnered with long time friend and co-founder of Studio 54, Ian Schrager to transform the 123 year-old Gramercy Park Hotel with minimalist architect John Pawson.
610 Lexington
In 2006, Rosen announced plans to develop the site at 610 Lexington Avenue in NYC (situated directly behind the Seagram Building) into a glass hotel and condominium tower designed by Sir Norman Foster.