One of his biggest passions over the years, however, has been aviation.
When he was young, his father was named the associate director of libraries at the University of Washington.
“I’d spend hours reading about the engines in some of those planes,” Allen told Forbes. “I was trying to understand how things worked — how things were put together, everything from aeroplane engines to rockets and nuclear power plants. I was just intrigued by the complexity and the power and the grace of these things flying.”
Allen started collecting planes and other World War II artifacts in the 1990s. In 2004, he opened his 31-piece collection — rumoured to be worth many millions of dollars — to the public. It’s currently housed in the Flying Heritage Collection, in a hangar in Everett, Washington.
Allen's collection includes two types of British planes that served in WWII. The Supermarine Spitfire has often been credited with winning the Battle of Britain. This particular plane was heavily damaged during a raid on enemy territory, though it has since been restored.
The Hawker Hurricane destroyed more enemy aircraft than any other British plane. This plane never saw combat and was recovered from a farm in Ontario, Canada, not far from where it was manufactured.
He also owns a number of German planes, some of which were actually used by pilots during WWII. The Fieseler Storch was named for the German word for 'stork' because its wings could be folded down to be transported by train.
This Focke-Wulf 190 was flown by a German pilot who crashed in a field and was taken prisoner by the Russians. Amazingly, the plane was discovered intact by a hunter in the 1980s, and it was airlifted to be restored by experts in England.
This Focke-Wulf 190 was the only long-nosed model of the plane to survive the war. It's in flyable condition, but it won't ever be flown because of how rare it is.
The Messerschmitt 163 Komet was the first operational rocket-powered aircraft, and this model is one of only a dozen in existence.
This Messerschmitt BF 109 E-3 disappeared during a WWII battle over the English Channel. It was discovered in 1988, when a man walking on the beach near Calais, France saw the tip of the plane's wing sticking out of the sand.
The Japanese Mitsubishi A6M Zero could outpace and outmaneuver most other planes. This plane was discovered in a wreck in New Guinea, but restoration work has made it flyable again.
The Nakajima 'Oscar' plane was a favourite of Japanese Kamikaze pilots during WWII. This plane was found in a dense jungle area shortly after the end of the war. Its front end was damaged from the crash, but workers were able to repair it with salvaged parts.
The Russian Ilyushin II-2 was known as 'Black Death' by enemy fighters. This plane crashed in 1944 after being hit by anti-aircraft fire. When it was discovered by scouts near a lake in 1991, it still had rockets and bombs attached to its wing.
The MiG-29 Fulcrum was created by the Soviet Union's Mikoyan Design Bureau to challenge American fighter pilots in the 1970s.
This Russian Polikarpov I-16 was found in 1991 and restored in the same factory where it was manufactured. Some of the workers who had originally built the plane aided in the restoration work.
The Polikarpov U-2 became famous as the plane flown by Russian women who made attacks on German camps late at night. Though they caused little destruction, the midnight attacks had a demoralizing effect on German troops.
The Curtiss JN-4 Jenny was the first mass-produced American plane and was used by Amelia Earhart and Charles Lindberg during early 20th-century training sessions. Allen's model was built in 1918 and is one of very few remaining Jennys in the world.
This plane is the only P-40C Tomahawk still in flying condition. It spent nine months defending the Russian front from German forces during WWII, but was hit by enemy fire in 1942.
This Grumman Hellcat was used during training for battles in the Pacific. It's one of only a few Hellcats remaining.
The B-25 was the first American plane to bomb the Japanese mainland. This particular plane was built in 1944, then served with the Royal Canadian Air Force for 10 years.
This P-51 Mustang was flown by American pilot Lt. Harrison B.'Bud' Tordoff during the liberation of Europe. Tordoff was reunited with the plane for the first time during a visit to the Flying Heritage Collection in 2003.
The P-47D Thunderbolt was considered by many WWII pilots to be 'unbreakable,' in part because of its heavy armour and powerful engine.
The White Knight was designed to be the launch vehicle for SpaceShipOne, a manned spacecraft funded by Allen and aerospace engineer Burt Rutan. During flights in 2003, 2004, and 2005, the White Knight carried the 8,000-pound spacecraft to an altitude of 8.7 miles.
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