[6] He started building Klarna at age 23[7] and co-founded the company with Niklas Adalberth and Victor Jacobsson in 2005.

[9] The Swedish Financial Sector Union expressed regret to have learnt about the job cuts from the media rather than being consulted beforehand and sued the company over the layoffs.

[6] In December 2024, he stated that the company stopped hiring people last year because "AI can do all of the jobs that we humans do.

[11] Siemiatkowski married Nina, a marketing executive he first met while attending the Stockholm School of Economics, in 2014.

She is the founder of a digital platform to connect donors with local nonprofits and played a key role in identifying a marketing agency that created Klarna's branding.