Sikorsky :

Sikorsky Aircraft is part of the Defense Systems Group of United Technologies Corporation. The company was founded in 1923 by Igor Sikorsky as the Sikorsky Aero Engineering Corp, and has been affiliated with UTC since 1929 when it moved to Stratford , Conn. , from Long Island .
In the 1920s and 1930s Sikorsky produced land-based aircraft, amphibians and flying-boats, including the flying Clippers, which pioneered commercial transoceanic air routes.

Since the early 1940s, Sikorsky has concentrated its efforts on helicopters.

By 1996, has produced more than 7800 rotary-wing aircrafts; further 1800 built by foreign licensees

Agusta :

Giovanni Agusta was one of the pioneers of the Italian aeronautical industries. He builds his first plane in 1907 and in 1923 he founded Construzioni Aeronautiche Agusta Spa.
In 1952 he begun to built helicopters with license, first from Bell , and then from Sikorsky and later the company start with its own models.

Bell :

In the early 1930's, Arthur Young, a brilliant young inventor, built and successfully demonstrated a viable, flyable, helicopter, model.
Larry Bell, a successful entrepreneur and founder of the Bell Aircraft Corporation , was so impressed with Young's efforts that in 1941 he set the youthful inventor up in a small shop in Gardenville , New York

At that time Bell was already a manufacturer of conventional aircraft such as the WWII fighter P-39 Airacobra and the P-59, America 's first jet-powered airplane. In addition, Bell was to develop the X-1, which was to become the world's first super- sonic plane.

By 1951, Bell helicopters were in service around the world, breaking records as fast as they were setting them. And since Bell Aircraft Corporation's reputation for helicopter manufacture began to rival its reputation as a builder of conventional aircraft, the company created a separate helicopter division which was headquartered in Fort Worth , Texas .