John Knudsen 'Jack' Northrop (November 10, 1895 - February 18, 1981) was an American aircraft industrialist. He co-founded the Lockheed Corporation in 1927. He was the founder and eponym of the Northrop Corporation in 1939.

Northrop's first job in aviation was in working for Loughead Aircraft Manufacturing Company (laterLockheed Corporation) in 1916. In 1923, Northrop joined Douglas Aircraft Company. He became chief engineer, but later rejoined Loughead — now renamed Lockheed. During his second tenure there, he worked on the Lockheed Vega, the civilian transport flown by Amelia Earhart.

In 1928, Northrop struck out on his own, founding the Avion Corporation, which Northrop was forced to cell to United Aircraft and Transport Corporation in 1930. In 1932, Northrop, backed by Donald Douglas of Douglas Aircraft, founded another company, the Northrop Corporation, in El Segundo, California. This company built two highly successful monoplanes, the Northrop Gamma and Northrop Delta .

By 1939, the Northrop Corporation had become a subsidiary of Douglas, so Northrop founded another completely independent company of the same name in Hawthorne, California. While working at this company, Northrop focused on the flying wing design, which he was convinced was the next major step in aircraft design. He produced a number of flying wings, including the Northrop N-1M , Northrop N-9M, Northrop YB-35, and Northrop YB-49.