H. Dale Hemmerdinger is the chairman of Atco Properties & Management, a family-run, New York City-based development firm. He took over the business in 1967, after the death of his father, Monroe Hemmerdinger.

In order to provide hedging opportunities for Atco and other real estate investors, he created a fund that buys and sells US property securities, Atlas Real Estate Fund, in the 1990s.

Former New York State governor Eliot Spitzer appointed him the chairman of the Metropolitan Transport Authority in 2007 and he served in that role until 2009. Hemmerdinger is a trustee of New York University and the New York City Police Foundation, serving as secretary and treasurer and chairman of the board.

He is a licensed New York State Real Estate Broker, a graduate of the selective, college-preparatory Riverdale Country School, and received a BA from New York University. He is married to Elizabeth Hemmerdinger, an Atco executive and playwright, with whom he has two adult children. The Hemmerdingers live on Central Park South and own a house in Rye, Westchester County. Their son Damon and daughter Katherine are co-presidents of the family firm.