Wilhelm J. D. Keuffel and Herman Esser were partners in the firm of Keuffel & Esser which was founded in July 1867.  The firm was incorporated in New Jersey in February 1889 and became Keuffel & Esser Company.   They first manufactured surveying instruments in 1885.

Wilhelm J. D. Keuffel was born at Walbeck in Thuringen, Germany in 1838 and died in Hoboken, New Jersey in 1908.  Herman Esser was born at Wuppertal-Elberfeld, Germany in 1845.  He retired from Keuffel & Esser Co. in 1902.  He was back in Bad Godesberg am Rheim, Germany in April of 1902 and died there in April 1908.

Reference:  Smart, Charles E.   The Makers Of Surveying Instruments In America Since 1700  Troy, New York:  Regal Art Press.  1962