The portrait is of James N.B. Hill, a member of the EYC from 1932 - 1975, and a life-member from 1954, pictured in his WWI naval reserve uniform.  He was the grandson of the famous, James J. Hill, known as the "builder of the Northwest Empire," as president of the Great Northern Railway, from St. Paul to Seattle.  It was the only privately funded and successfully built transcontinental railway in U.S. history.  James N.B. Hill led a bachelor's life between the Tennis and Racquet, the Eastern Yacht Club and finally the Ritz in Boston, where he died in 1975. 

Pictured below are the paintings he gave to the Eastern.