Belgian computer scientist Pieter Wuille first heard about Bitcoin in 2010, and started contributing to Bitcoin Core (Bitcoin’s reference implementation, then called Bitcoin-Qt) in 2011. In 2014, he left his job at Google in Switzerland to make Bitcoin development his full-time focus.
Wuille was first granted commit access to the Bitcoin Core repository in 2011, a position he held until 2022. Over these years, Wuille contributed tens of thousands of lines of code to the Bitcoin Core codebase. (For context, this is in the same ballpark as Bitcoin creator Satoshi Nakamoto himself.)
Many of his contributions have been instrumental in keeping Bitcoin Core usable and accessible while growing adoption tested the limits of what the software could handle. Wuille was for example the initial author of the secp256k1 library for elliptic curve math used in Bitcoin, based on experimental code originally published by Hal Finney, which made signing and verifying signatures massively faster and more secure. Similarly, he helped migrate Bitcoin to a faster database backend, LevelDB. He also developed ultraprune, which minimized the amount of data Bitcoin nodes need to keep track of while syncing with the network, and he developed parallel script verification, which significantly sped up block verification.
Besides scalability improvements, Wuille also helped add many new features to the Bitcoin Core software. He for example developed reindex, which lets users rebuild Bitcoin’s block index (useful when recovering backups); he designed hierarchical deterministic wallets, which allow users to back up their private keys with a single seed phrase; he co-created MiniScript, making it easier to program more complex types of transactions; he helped facilitate the upgrade to Tor v3, helping Bitcoin users preserve their privacy; he designed Bech32 addresses for more efficient block space use; and much more.
But perhaps most notably of all, Wuille was largely responsible for the development of Segregated Witness (SegWit), the biggest Bitcoin protocol upgrade to date. SegWit offers several benefits, including increased transaction throughput on the Bitcoin network and a fix of the long-standing transaction malleability bug, which in turn readied the Bitcoin protocol for the deployment of the Lightning Network, the Layer 2 protocol for fast and cheap transactions.
Overall, Wuille has been a driving force within the Bitcoin development community throughout the project’s 16-year history — and during the second halving epoch in particular — as he helped shepherd the project from a niche internet currency to a serious alternative to the existing monetary system used by millions of people around the world.
Gregory Maxwell had been interested in electronic cash even before the invention of Bitcoin: In the mid-2000s, the Californian software developer contributed to RPOW, the digital currency project Hal Finney created.
When he first heard about Bitcoin in 2010, Maxwell quickly realized that Satoshi Nakamoto’s electronic cash system accomplished something he’d deemed to be impossible: Despite the network’s distributed nature, users could come to consensus over the state of the ledger. Maxwell began contributing code to Bitcoin Core in 2011, and in 2012 was granted commit access to the project. He stepped down from this position for personal reasons in late 2015, but continued contributing code and review.
Early on, Maxwell considered improving Bitcoin’s privacy features a core objective for himself and the project as a whole, and led the charge in researching various solutions to enhance this. Perhaps most notably, Maxwell is the inventor of the privacy technique CoinJoin, which allows multiple users to merge their transactions into a single, bigger transaction, thereby obfuscating the trail of coin ownership on the blockchain. CoinJoin would go on to be used in several mixing services and other Bitcoin privacy projects.
Maxwell also led research into implementing Schnorr signatures in Bitcoin, which would enable additional privacy solutions and offered the potential to make existing privacy features more cost-efficient. Schnorr signatures were ultimately added to the Bitcoin protocol through the Taproot upgrade, which he also originally proposed.
Besides privacy, Maxwell contributed important scalability research. Like Wuille, Maxwell helped develop the secp256k1 library, he explored how to speed up sync-time for Bitcoin nodes, he thought of ways to improve block propagation efficiency, and more.
On top of his contributions as a software developer, Maxwell during these formative years of Bitcoin’s existence also took an active role in communicating Bitcoin’s potential and limitations to other developers and regular Bitcoin users alike.
As pressure started mounting from (in particular) some of the more commercially oriented Bitcoin businesses to increase the block size limit in order to boost on-chain transaction throughput, he, for example, knew how to articulate why deploying such a contentious backward-incompatible hard fork upgrade posed an existential threat to the project, and why backward-compatible soft fork upgrades were preferable.
Likewise, he outlined the importance for regular users to remain fully validating peers on the network to retain Bitcoin’s decentralized and trustless security properties, and effectively communicated how Bitcoin could still scale through Layer 2 protocols like the Lightning Network.
All in all, during the second halving epoch Maxwell established himself as one of the most — and perhaps the most — influential developers in Bitcoin’s short history.
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In 2014, together with several other Bitcoin Core contributors and digital cash pioneers, Maxwell and Wuille co-founded Blockstream, a Canadian blockchain research and development company that supported Bitcoin Core development at a time when few other organizations did. Blockstream has over the years also created the Liquid sidechain and developed the Core Lightning software implementation; maintains the Green wallet; produced the Jade hardware wallet; engaged in Bitcoin mining, and more.
Today, Wuille is an engineer at Bitcoin development company Chaincode Labs in New York City and continues to write Bitcoin code.
Maxwell has largely retired from Bitcoin development, but he has in recent years invested significant time and effort in defending Bitcoin Core developers and other industry players as they were being harassed through frivolous but expensive lawsuits.
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