Sebastian Siemiatkowski

Working a Burger King register at fifteen, Sebastian Siemiatkowski noticed that customers reached for credit far more often than debit, and started wondering why. He met one of his future co-founders behind the same counter.¹

Siemiatkowski is the co-founder and chief executive officer of Klarna, a Swedish fintech company providing buy-now-pay-later checkout financing and payments infrastructure for online retailers. Klarna sits between shopper and merchant at the point of sale: it pays the merchant immediately, then collects from the consumer later, absorbing the credit and default risk for a fee. Founded in Stockholm in 2005, it grew into one of Europe's most prominent private fintech companies before listing on the New York Stock Exchange in 2025.

Background

Siemiatkowski was born on October 3, 1981, in Sweden, to parents who had fled Poland in 1980 during the Solidarity era and settled in Uppsala; he considers himself a second-generation Polish immigrant. Immigration bureaucracy forced the family to leave his older sister behind in Poland for about a year. His father had trained as a veterinarian in Poland but worked as a taxi driver and food inspector in Sweden, a credential downgrade common among Eastern European emigrants of the period. His mother, who had a back injury, later worked as an artist.

The household knew real poverty; Siemiatkowski has said the family sometimes went weeks at a time on Swedish pancakes made only of flour and milk.¹ His parents had an on-and-off marriage and separated when he was about eight. He credits a Swedish policy subsidizing computer ownership for giving the family its first computer, and read widely at the library with his father, including biographies of IKEA's Ingvar Kamprad and Virgin's Richard Branson, which he says nurtured his interest in business. He attended Katedralskolan in Uppsala and later earned a master's degree from the Stockholm School of Economics. At fifteen he worked at Burger King, a formative education in thin-margin retail operations, where he met future Klarna co-founder Niklas Adalberth.

Getting started

Siemiatkowski met his third co-founder, Victor Jacobsson, as a classmate at the Stockholm School of Economics. During a sabbatical he attempted to circumnavigate the globe without flying, taking odd jobs including bartending and waiting tables at a ski resort. Stranded in Sydney after missing his cargo ship connection to Los Angeles, he worked as a furniture mover to survive, later saying it proved to them that "no matter how bad things looked, we could find a way to survive."¹

Back in Sweden, he missed his re-enrollment deadline, was briefly on welfare, and took a telemarketing job selling invoice factoring to small businesses. Through that work he saw ecommerce merchants, overwhelmed by payment risk, demanding upfront or debit payment because they could not absorb chargebacks and returns. The founding insight: insert a better-capitalized intermediary that pays the merchant immediately at checkout and collects from the consumer afterward. An early pitch competition rejected the idea, with judges reportedly saying it would never work, but the founders continued anyway.¹

What he built

Siemiatkowski co-founded Klarna in Stockholm in 2005 with Niklas Adalberth and Victor Jacobsson. The company expanded from Sweden across Europe and then into the United States, becoming through the 2010s and early 2020s the largest and most prominent European private fintech company.

Sequoia Capital led a round in 2010, taking roughly a quarter of the company. SoftBank led a 2021 round valuing Klarna at $46 billion, its peak private valuation and the highest ever for a European fintech.¹ In July 2022, amid a market reset for buy-now-pay-later, a down round raised $800 million at roughly $6.7 billion, about an 85 percent discount from peak. Total private capital raised exceeds $4 billion. Klarna filed confidentially in November 2024 and listed on the NYSE on September 10, 2025, under ticker KLAR, pricing above range at $40 a share and closing its debut at roughly $17.3 billion; Siemiatkowski did not sell shares in the offering.² By the mid-2020s Klarna served tens of millions of consumers and hundreds of thousands of merchants, with a workforce of roughly 5,000 after restructuring in 2023 and 2024.

How he operates

Siemiatkowski describes himself as a salesman-founder rather than a quant or product visionary. "I always loved polishing and refining my sales script," he has said. "Eventually I knew I got it perfect one day when I closed 16 calls in a row." He finds sales, a trade often dismissed as a lowlife pursuit, beautiful. He emphasizes founder-team complementarity, describing Adalberth as the one who could show him he was wrong in a youth spent convinced he was right.³ He positions Klarna's mission as a smoother way to shop and financial inclusion for an outsider, drawing on his family's precarity as motivation. In the 2020s he became a vocal proponent of using generative AI aggressively inside Klarna's operations, including customer service automation and headcount reduction. His focus stayed on the financing and payments layer beneath ecommerce rather than on a consumer retail brand of his own.

Where things stand

As of Klarna's September 2025 listing, Siemiatkowski remained chief executive and a significant shareholder. Klarna is now public on the New York Stock Exchange, valued at roughly $15 billion to $17 billion at listing, well below its 2021 peak but a completed IPO after the 2022 down round. He continues to push Klarna to be AI-native and to position buy-now-pay-later and checkout financing as core consumer payments infrastructure.²

Key facts

• Born October 3, 1981, in Sweden to Polish refugees who fled communism in 1980; the family at times survived on flour-and-milk pancakes.
• Worked at Burger King at fifteen, where he met eventual Klarna co-founder Niklas Adalberth.
• Took a round-the-world trip without flying as a sabbatical, got stranded in Sydney, and worked as a furniture mover to survive.
• Discovered the Klarna model doing telemarketing for an invoice-factoring company after missing his re-enrollment deadline and going on welfare.
• Co-founded Klarna in Stockholm in 2005 with Adalberth and Victor Jacobsson at age 23 to 24.
• Klarna reached a $46 billion valuation in 2021, fell to roughly $6.7 billion in a 2022 down round, and listed on the NYSE in September 2025 at roughly $15 billion to $17 billion.