Pieter Wuille found Bitcoin in December 2010 and began contributing code in May 2011. Chaincode Labs, where he works as an engineer, records that he has written significant parts of the reference client, particularly on performance and code organisation, and that he has authored or co-authored sixteen Bitcoin Improvement Proposals.
The most consequential of his libraries is libsecp256k1. The Bitcoin Core 0.10.0 release notes describe it as "created by Bitcoin Core developer Pieter Wuille" when the project moved signing away from OpenSSL in February 2015, and the 0.12.0 notes credit him with the pull request that switched signature validation over a year later. He also contributed to the design of Miniscript, co-authored papers on MuSig and Bulletproofs, and worked on ctaes and minisketch.
Before Chaincode he was a co-founder and Core Engineer at Blockstream, and a Site Reliability Engineer at Google. He holds a PhD in Computer Science from the University of Leuven, where his work was on programming language design.