Everybody knows Microsoft cofounder Bill Gates, the second-richest man in the world.
But Microsoft’s other cofounder, Paul Allen, only became famous outside of Seattle once he published his memoirs in 2011.
He too was rich, and his net worth was pegged at $20 billion. With his money, he invested in a lot of tech companies, real estate, and art. But he also led an over-the-top life filled with rock and roll parties, collections, yachts, and sports teams.
Allen died on Monday aged 65 after a battle with cancer. Here is a look back at his fabulous life.
Can you spot Paul Allen from this famous photo of Microsoft's earliest employees?
He's the guy in the bottom right.
Allen met Bill Gates in high school, where they hacked the school computer to try and help Gates meet girls.
Allen and Gates hacked the computer at Lakeside school to enrol Gates in classes where he was the only boy, Gates told the BBC in a 2016 interview.
It was Allen who first came up with the name "Micro-Soft."
Allen also suggested to Gates that they work together on what would become Microsoft's first product, a BASIC language interpreter for the Altair 8800 microcomputer.
He didn't just party with rock stars, he jammed with them.
Allen played guitar, and in his own band, "The Underthinkers," who cut an album in 2013. Allen wrote or cowrote every song on it.
According to gossip in the Seattle music scene, he kept several musicians on full-time retainer. They had to be ready to hop on a plane and fly anywhere in the world to jam with Allen and rock star party guests like Eric Clapton.
The album featured guest performers Ann and Nancy Wilson of Heart, Chrissie Hynde, Joe Walsh, Derek Trucks, Doyle Bramhall, David Hidalgo of Los Lobos, Ivan Neville, and others.
He built a museum devoted to his rock hero.
In 2000, Allen opened the Experience Music Project, a rock and roll museum dedicated to his hero Jimi Hendrix and housed in a psychedelic Frank Gehry building that was meant to look like a melted guitar.
EMP has since grown into a full-fledged interactive museum, now known as the Museum of Pop Culture. It has exhibits that cover everything from Nirvana to "The Wizard of Oz" and Marvel.
Music producer Quincy Jones once compared Allen's musical talent to Jimi Hendrix.
In an interview in which the producer called the Beatles "the worst musicians in the world," Quincy Jones said that Paul Allen could play guitar and sing "just like" Jimi Hendrix.
He owned two professional sports teams, and part of a third.
A lot of billionaire moguls own a professional sports team, but Allen owned two: The Portland Trail Blazers basketball team, which he bought in 1988, and the Seattle Seahawks football team, which he bought in 1997 after Ken Behring threatened to move the team to California.
He was also part owner of the Seattle Sounders FC.
He collected vintage WWII fighting planes.
Paul Allen collected all kinds of other stuff, too, including vintage airplanes. Here's a picture from 2008, when he opened his collection of WWII planes to the public.
His art collection was more than just a hobby; it was a business.
A Mark Rothko painting owned by Allen sold for a jaw-dropping $56.2 million at auction. Allen bought the work for $34.2 million in 2007.
He also sold a William de Kooning painting for $35 million in March 2018 to a private collector in Hong Kong.
He owned multiple super yachts.
Allen owned three superyachts: Octopus, Meduse, and Charade - where Bill Gates reportedly spent his honeymoon. He also owned the expedition yacht Tatoosh.
The Octopus played host to some wild New Years' parties and visits from recording artists like Mick Jagger and Damian Marley. It was also a regular party venue for the Cannes film festival.
The Octopus is huge...
It has its own submarine.
The submarine can sleep 10 people for up to two weeks.
Guests got to take a look around the yacht, including the submarine Allen keeps onboard. [Here's a photo posted to Instagram of it.]
He owned a research vessel which found the wreck of a WWII warship.
The Research Vessel Petrel found the wreck of the USS Indianapolis in 2017, a warship whose sinking was a devastating loss for the US in the Pacific.
He also found a sunken Japanese warship in the Phillipines with a remote operated probe.
Allen posted pictures on Twitter in 2015 of the WWII battleship Musashi, with the line "RIP (rest in peace) crew of Musashi, approximately 1,023 (lives) lost."
He founded a space startup to build the world's largest plane.
Allen cofounded Stratolaunch Systems, a startup looking to make spaceflight more affordable by using huge lightweight planes to launch people and cargo off the ground. It then launches rockets into space from 30,000 feet.
Stratolaunch first unveiled the world's largest plane in 2017. Its wingspan is 385 feet, which is is longer than a football field, and you can take a look inside here. It has yet to take its first flight.
He also collected mansions.
Like many other wealthy billionaires, Paul Allen had a quite the real estate portfolio, buying mansions everywhere he needed a landing spot.
Shortly after his investment company, Vulcan Capital, opened a Palo Alto office, Allen bought a gorgeous $27 million, 22,000-square-foot mansion nearby in Silicon Valley's most expensive town of Atherton.
The six-bedroom house also had a separate two-bedroom guest house and a five-car garage with a "manager's suite."
He sold a Malibu mansion because of the sound of the ocean.
Allen sold his $28 million Malibu home on Carbon Beach, also known as Billionaire's Beach.
Allen paid $25 million for the home in 2010, though the rumor was that he didn't like staying at the home because he "hated the sound of the ocean."
He also sold his private island.
In late 2013, Allen also sold his 292-acre private island off the coast of Washington for a mere $8 million.
Allen had reportedly tried to sell the island for years, first listing it in 2005 for $25 million and dropping the price to $13.5 million in 2011.
His home in Seattle was also amazing.
Allen's home in the Seattle suburb of Mercer Island was a 10,000-square foot compound hidden in the trees with quarters for his mother and a regulation NBA size basketball court.
That octagonal shape on top of the yacht is a helicopter landing pad.
He bought his favorite movie theater when it was going to be demolished.
He refurbished The Cinerama, a 70mm movie theater, with state of the art sound and projection systems while preserving its vintage curved screen.
His Vulcan investment firm also helped to redevelop some of the formerly seedier parts of Seattle over the past decade into some of the coolest, most trendy parts of the city.
Allen's investment firm Vulcan has stakes in tech giants.
The company has stakes in private firms like Uber, as well as giant listed companies including Facebook and Amazon.
He founded an institute devoted to brain science.
Allen funded tons of charitable projects, including The Allen Institute for Brain Science, which regularly releases research about the brain for free on the website brain-map.org.
He lured one of Seattle's most successful entrepreneurs into a job.
Allen also launched a second, somewhat related foundation known as the Institute for Artificial Intelligence, or AI2. He then lured Oren Etzioni, one of the big names in the Seattle-area tech scene, into running AI2.
Together Allen and Etzioni wanted to create a computer so smart it could take classes and pass tests designed for humans. Etzioni said that working for Allen was fantastic.
He's given over $2 billion to charity.
In addition to his two institutes, Allen gives millions to other charitable causes. As of October 2018, Allen has given away more than $2 billion to charity in his lifetime. In 2011, he gave away $327.6 million, making him the most generous American of that year.
He gave to worldwide projects like Ocean research and African wildlife preservation, particularly an elephant-saving organization called Elephants Without Borders.
His Paul G Allen Family Foundation gives to regional and local causes affecting the Seattle area with a focus on music, art, youth, and education.
He died aged 65 after a battle with cancer
Paul Allen passed away aged 65 after a battle with non-Hodgkin's lymphoma, having first been diagnosed in 2009 and going through a period of remission. Allen had previously survived Hodgkin's lymphoma when he was diagnosed in the 1980s.
Bill Gates said he was "heartbroken" by the news of Allen's death.
"Paul loved life and those around him, and we all cherished him in return. He deserved much more time, but his contributions to the world of technology and philanthropy will live on for generations to come. I will miss him tremendously," said Gates.
Tech leaders paid their respects to Allen.
Tim Cook, Jeff Bezos, and Sundar Pichai released statements marking Allen's passing. Cook said: "Our industry has lost a pioneer."