In 1963 the US Airforce started a series of test on large transport aircraft. The biggest at the time was the C-141 Starlifter, but much larger aircraft was needed. The first designs to come out had six engines but thier studies confirmed that they would need special made engines and a special airframe.
By 1964 many aircraft companies sent the designs to Boeing and engine manufactures sent thiers in as well.
After carefully studing each design Boeing went with a combanation of Lockheeds design for the airframe with General Electric's engine design.
Juan Trippe(the president of Pan AM) asked boeing to create and airplane twice the size of the 707, so boeing and Pan Am worked together to create the 747 design out of the transport design in 1964.
For thier work in the design Boeing sent the first 747 to Pan Am.
Before the first 747 was fully assembled, testing began on many components and systems. One important test involved evacuation of 560 volunteers from a cabin mock-up via the plane's emergency chutes.
On 30 September 1968, the first 747 was rolled out of the Everett assembly building before the world's press and representatives of the 26 airlines that had ordered the plane. Despite a minor problem with one of the flaps, the flight confirmed that the 747 handled extremely well. The plane was found to be largely immune to "Dutch roll", a phenomenon that had been a major hazard to the early swept-wing jets.
On 15 January 1970, First Lady of the United States Pat Nixon christened Pan Am's first 747 at Dulles International Airport in the presence of the Pan Am chairman.The 747 entered service on 22 January 1970, on Pan Am's New York–London route; the flight had been planned for the evening of 21 January, but engine overheating made the original aircraft unusable. Finding a substitute delayed the flight by more than six hours to the following day.
When economic problems in the United States and other countries after the 1973 oil crisis led to reduced passenger traffic, several airlines found they did not have enough passengers to fly the 747 economically, and they replaced them with the smaller and recently introduced McDonnell Douglas DC-10 and Lockheed L-1011 TriStar wide bodies (and later the twinjet 767 and A300).
Today the 747 is still not as popular as once before but i has over 9 variants including the "Dreamlifter" and Air Force One.
British airlines has the biggest fleet of 747's at a count of 57 aircraft.