Microsoft's Other Founder: Paul Allen and the 1975 Story

If the question is who, officially, was the other founder of Microsoft alongside Bill Gates, the short answer is: Paul Allen. But the name alone hides the best part of the story. It was Allen who saw the January 1975 cover of Popular Electronics, persuaded Gates to drop out of Harvard and wrote the code that made BASIC run in Albuquerque. It's worth knowing the rest.

TL;DR

• The other founder of Microsoft is Paul Gardner Allen (1953–2018), Bill Gates's partner since their days at Lakeside School in Seattle.
• The company treats 4 April 1975 as its official founding date, in Albuquerque, New Mexico.
• The name "Micro-soft" first appears in writing in a letter from Gates to Allen dated 29 July 1975, recorded on Microsoft's own official timeline.
• Allen left the company in 1983 after being diagnosed with Hodgkin lymphoma, and died on 15 October 2018, aged 65.
• His technical legacy lives on in the AI of 2026: the Allen Institute for AI (Ai2) publishes the Olmo family with open weights, data and code.

Who was the other Microsoft founder according to official documentation

Paul Gardner Allen. Born in Seattle in 1953, two years older than Bill Gates, his fellow member of the Lakeside School computer club and partner in an earlier venture before Microsoft. When the pair sold their first program, Gates was 19 and Allen was 22 — Microsoft itself describes the episode in historical material published on Microsoft Learn.

Anyone searching for the other Microsoft founder usually stumbles across three wrong names before hitting the right one. First, Steve Ballmer: he joined in 1980, became CEO in 2000 and stayed for 14 years, but he was never a founder. Second, Ed Roberts of MITS, the maker of the Altair 8800 — he was the first customer, not a partner. Third, Monte Davidoff, the Harvard student who wrote the floating-point package for Altair BASIC: a crucial contributor, but with no equity stake.

None of the three is the other Microsoft founder in the corporate sense. The official answer is unambiguous: alongside Bill Gates, the other founder of Microsoft was Paul Allen. And the division of labour between the two is what explains why the company succeeded.

1975 in order: the timeline Microsoft itself records

The chronology below comes from the company's historical documentation and shows what the other Microsoft founder did at each stage of that year. It's useful because it debunks a common myth: the company wasn't born from a business plan; it was born from a product sold before the partnership formally existed.

Date	What happened
January 1975	The MITS Altair 8800 appears on the cover of Popular Electronics. The article convinces Allen and Gates to write a BASIC for the machine.
February 1975	The two complete Altair BASIC and sell it to MITS in Albuquerque — their first customer. It's the first computer language program for a personal computer.
March 1975	Paul Allen joins MITS as director of software.
4 April 1975	Official founding date of Microsoft, as a partnership between Gates and Allen, in Albuquerque.
7 April 1975	"Altair BASIC – Up and Running" is the headline of the first issue of MITS Computer Notes.
1 July 1975	The pair's BASIC is officially distributed as version 2.0, in 4K and 8K editions.
22 July 1975	Allen and Gates sign the licensing agreement for the BASIC interpreter with MITS. The name "Microsoft" doesn't exist yet.
29 July 1975	In a letter to Paul Allen, Gates uses "Micro-soft" — the earliest written reference known.
31 December 1975	The year's revenue closes at US$16,005, according to the partnership's Form 1065 tax return.

Notice the sequence: product sold in February, partnership formalised in April, name defined in July, five-figure annual revenue in December. No unicorn started any differently — what changes is the yardstick used by those who tell the story later.

The name, incidentally, is a fusion of microcomputer and software, and the credit for the idea is usually attributed to Allen. The hyphen was dropped the following year. In 1979 the company moved from Albuquerque to Washington state, near home.

What the other Microsoft founder did that Bill Gates didn't

Here's the part the quiz doesn't ask, and which matters to anyone building a technical team.

The window-of-opportunity radar

Allen was the trend spotter. It was he who brought in the magazine, who identified that cheap microprocessors would create a market for personal software, and who insisted the window would close quickly. The second founder's role in this phase was to detect the timing — a skill that rarely appears on a CV and that decides a product's fate.

The engineer of the improbable

The technical detail is elegant: the pair wrote the BASIC interpreter for a computer they had never touched, using an emulator of the Intel 8080 processor running on a PDP-10 minicomputer. Allen wrote the loader that put the program into the Altair's memory. The demonstration worked on the first try, in Albuquerque, in front of the customer. Anyone who has deployed code to production without an identical staging environment knows the size of that risk.

The counterbalance in the partnership

Gates was the relentless negotiator of contracts and licences. Allen was the architecture and next-product guy. The company worked as long as the two roles were balanced. When the imbalance came — with illness and equity dilution — the partnership broke.

Why the second Microsoft founder left in 1983

Allen was diagnosed with Hodgkin lymphoma in 1982 and left Microsoft's operations in 1983, retaining his shareholding. He spent the next three decades doing other things: he bought the Portland Trail Blazers (NBA) and the Seattle Seahawks (NFL); funded neuroscience research with US$500 million for the Allen Institute for Brain Science; and donated more than US$2 billion over his lifetime.

He died on 15 October 2018, aged 65. The immediate cause was septic shock, a complication associated with the non-Hodgkin lymphoma he had been treated for since 2009.

There's an uncomfortable lesson here for technology business partners in the UK: a partnership agreement without a clear clause for departure due to ill health, without dilution rules and without an exit provision is a ticking time bomb. I've seen this happen in at least three agencies and software houses I've worked with in 17 years at Agathas Web. A hastily drafted shareholder agreement costs more than any tech stack.

Allen's legacy lives in the AI your business uses in 2026

This isn't rhetorical homage. The other Microsoft founder's money funded one of the most relevant research institutions in the sector. The Allen Institute for AI, Ai2, based in Seattle, is today one of the few institutions that publish fully open language models — weights, training code, checkpoints and datasets. The Olmo family follows this policy, and the Olmo 3.1 Think 32B and Olmo 3.1 Instruct 32B versions are distributed with training and fine-tuning data available without licence restrictions.

Why does this matter for a UK company? Because full openness is what allows you to audit bias, run the model on your own infrastructure and avoid being held hostage by a supplier's price or policy changes. When we evaluate a model for a customer service or document classification project, the criterion isn't just the benchmark: it's what happens to the client if the API price rises 40% or is discontinued.

Yes, that has happened — and it's not rare. We treat third-party dependency risk as an architecture item, not a legal detail.

Microsoft in August 2026: Copilot superapp and data centres in São Paulo

While the name of the other Microsoft founder resurfaces in searches, the company he helped create is in the middle of two concrete changes.

Copilot becomes a single app. On 13 August 2026, Microsoft confirmed it will unify its assistants into a single application called Microsoft Copilot, with a new icon. The migration began on mobile and web in mid-August and reaches desktop, on Windows and macOS, in mid-September. Two features were retired on 18 August 2026: the podcast tool and Deep Research. Groups, messages and extra content from those areas are not migrated. If your operation used Deep Research in a research routine, the deadline has passed — export anything that exists and review the workflow.

Infrastructure in Brazil. On 11 February 2026, at the Microsoft AI Tour, Microsoft Brazil's president, Priscyla Laham, announced that two cloud and AI data centres are already operating in São Paulo state, with construction completed in January. The exact location was not disclosed for security reasons. The investment is part of the R$14.7 billion package announced in September 2024, to be spent by 2027, alongside a goal to train 5 million Brazilians in AI.

Also in 2026, Microsoft created Microsoft Frontier Company, a US$2.5 billion unit with 6,000 specialists to deploy AI for corporate clients, led by Brazilian executive Rodrigo Kede Lima.

And Bill Gates, now 70, continues publishing: on 15 August 2026 he returned to the topic of AI applied to health, citing WHO data on the shortage of nearly 6 million health workers in sub-Saharan Africa. Half a century after the Altair, the two founders are still setting the agenda — one through what he writes, the other through what he funded.

What Microsoft's founding teaches UK SMEs

The decisions made by Gates and the other Microsoft founder in 1975 still fit into a 2026 business plan. Five lessons that survive the 51-year test:

1. Sell before you build the structure. BASIC was sold in February; the partnership came in April. Validating demand before setting up a company, team and office remains the right order.
2. Earn little without shame. US$16,005 in the first year. Those who expect a spectacular first year usually don't reach the second.
3. Asymmetric pairs win. One partner who sees the market and another who closes contracts is a better combination than two identical people.
4. Licensing is more profitable than a one-off sale. Microsoft licensed BASIC to MITS rather than selling the code outright. Fifty years later, it's exactly the same reasoning behind any SaaS.
5. Document the partnership. Allen's exit shows that agreements need to be written down before life happens.

This fifth point has direct resonance in the UK in 2026, with the growth of digital operations that start informally and only formalise after they start earning.

How we apply this logic in Agathas Web projects

I've been a full-stack developer for over 15 years and founded Agathas Web in 2008 — long enough to have seen three complete hype cycles. My reading of Microsoft's founding history is practical: technology becomes a business when someone turns technical capability into recurring contracts.

That's what we do on three fronts. In official WhatsApp API integrations, we set up the direct channel with Meta rather than going through a platform that marks up per message — the same principle of licensing rather than reselling. In Moodle and e-learning environments, we deliver Linux, Redis and cloud infrastructure sized for real access peaks, not for the supplier's brochure. In applied AI, we evaluate model by model, including open alternatives like those from Ai2, before tying a client to a single provider.

If you're assessing how AI actually enters your company's operations, I've written about what changes in practice for UK businesses and about AI agents in corporate routines. And if the topic is the infrastructure behind it, Microsoft's recent shift to Linux servers shows well how platform decisions affect the final cost.

Conclusion: the right name and the right lesson

Alongside Bill Gates, the other founder of Microsoft was Paul Allen — and the one-word answer is the least useful part of the story. What's worth retaining is the method: two complementary profiles, a product sold before the company existed, licensing instead of a one-off sale, and US$16,005 in first-year revenue.

If your operation is at that stage of turning technical competence into predictable income, start with the basics: choose a product that can be licensed, document the partnership and don't outsource the architecture decision. It's a conversation we enjoy having — and one that usually yields more than any search trend.