Jack Northrop founded three companies using his name. The first was the Avion Corporation in 1927, which was absorbed in 1929 by the United Aircraft and Transport Corporation as a subsidiary named "Northrop Aviation Corporation". The parent company moved its operations to Kansas in 1931, and so Jack, along with Donald Douglas, established a "Northrop Corporation" located in El Segundo, California, which produced several successful designs, including the Northrop Gamma and Northrop Delta. However, labor difficulties led to the dissolution of the corporation by Douglas in 1937, and the plant became the El Segundo Division of Douglas Aircraft.

Northrop still sought his own company and in 1939 established the "Northrop Corporation" in nearby Hawthorne, California, a site located by co-founder Moye Stephens.  It was in Hawthorne, California that the P-61 Black Widow night fighter, the flying wings (B-35 and YB-49), the F-89 Scorpion interceptor, the SM-62 Snark intercontinental cruise missile, and the F-5 Freedom Fighter economical jet fighter (and its derivative, the successful T-38 Talon trainer) were developed and built.

The F-5 was so successful that Northrop spent much of the 1970s and 1980s attempting to duplicate its success with similar light-weight designs. Their first attempt to improve the F-5 was the N-300, which featured much more powerful engines and moved the wing to a higher position to allow for increased ordnance that the higher power allowed. The N-300 was further developed into the P-530 with even larger engines, this time featuring a small amount of "bypass" (turbofan) to improve cooling and allow the engine bay to be lighter, as well as much more wing surface. The P-530 also included radar and other systems considered must-haves on modern aircraft. When the Light Weight Fighter program was announced, the P-530 was stripped of much of its equipment to become the P-600, and eventually the YF-17 Cobra, which lost the competition to the General Dynamics F-16 Fighting Falcon.

Nevertheless, the YF-17 Cobra was modified with help from McDonnell Douglas to become the McDonnell Douglas F/A-18 Hornet in order to fill a similar light-weight design competition for the US Navy. Northrop intended to sell a de-navalized version as the F-18L, but the basic F-18A continued to outsell it, leading to a long and fruitless lawsuit between the two companies. Northrop continued to build much of the F-18 fuselage and other systems after this period, but also returned to the original F-5 design with yet another new engine to produce the F-20 Tigershark as a low-cost aircraft. This garnered little interest in the market, and the project was dropped.

Based on the experimentation with flying wings the company developed the B-2 Spirit stealth bomber of the 1990s.  In 1994, partly due to the loss of the Advanced Tactical Fighter contract to Lockheed Martin and the removal of their proposal from consideration for the Joint Strike Fighter competition, the company bought Grumman to form Northrop Grumman.

Source: Wikipedia