This is an entry in CoinDesk's Most Influential in Blockchain 2017 series.
Pieter Wuille is quick to bite his tongue.
In one of the developer's first-ever long-form interviews, it's clear he has plenty of thoughts to share. He gets fired up when chatting about bitcoin's coming innovations and the cryptocurrency's original white paper.
"There's so much we've learned since then," he says, addressing those he feels treat the nine-page document, published in 2008, as a "bible" of sorts.
Over the span of just a few minutes, he lists several holes in the paper - so-called "fraud proofs" have been shown unlikely, or at least very difficult, to work, while it failed to predict key innovations, such as scripts and payment channels.
He's probably one of the few knowledgeable enough to pick apart bitcoin's guiding document. And yet, as he starts to speculate on how Satoshi Nakamoto's paper might look if drafted today, he stops mid-sentence.
"I really shouldn't speculate," Wuille says.
And when asked what he would do if Nakamoto appeared before him - after a pause - Wuille says, "I would say, 'Thank you.'"
In these moments of hesitation, these flashes of deliberation, the shy developer decides it's better to keep his focus on the facts than let his opinions be used in the political barrage that bitcoin's raging scaling debate has become.
These moments, they define Pieter Wuille, alongside his six years of servitude, working tirelessly on Bitcoin Core, the currency's most popular software implementation (as well as the term often used to denote the loose group of volunteers that make changes to this code).
Following Wladimir van der Laan, bitcoin's lead maintainer, Wuille has made the second-most contributions to the software, but it's safe to say he's been behind some of the more significant changes. One particular upgrade, Segregated Witness (SegWit), came to define this year's scaling debate.
The groundbreaking (and highly controversial) change, enacted in August, shook the bitcoin community this year, where tensions were high and social media was a firestorm of finger-pointing and slander.
You'd think the creator of the code change would get involved and defend its creation, but actually Wuille seemed too cool and collected to stoop to such levels.
According to developer Nicholas Dorier:
"Pieter is trying to put aside all politics and always look only at the technical aspects of things."
This is likely why you can sense a cringe when he's asked how much bitcoin he owns, and why he says he couldn't think of any truly defining stories over his years of working on bitcoin. His personal website is bare, with just a spinning email icon whose pixelated graphics look straight out of the 1990s.
Wuille seems to cherish his privacy.
It makes sense, many bitcoin enthusiasts came to the cryptocurrency that way, but becoming one of the most well-respected developers, that was something that only someone as poised and focused as Wuille could pull off.
But his story begins with another computer scientist and notable cypherpunk, the late Hal Finney, the recipient of bitcoin's first-ever transaction.
In 2011, Finney - who unlike other jaded cypherpunks at the time was keeping an open mind to bitcoin - submitted a contest (with a 20 bitcoin prize) to a popular bitcoin talk forum. A cryptographic puzzle, it was designed to test developer understanding of the nascent currency.
And Wuille quickly got to work.
This was the first time Wuille, who had a PhD in computer science and a job at Google behind him, looked over the bitcoin codebase. Like many other programmers, Wuille's interest was piqued on a technical level - initially the code looked like a mishmash, but he marvelled that bitcoin actually worked (after so many failed decentralized money plays).
And in turn, he put together a solution - his first shot at bitcoin development, a moment that would change his life, and the trajectory of bitcoin, forever. Yet, that wasn't his shining moment.
"I don't remember who won, but it wasn't me," Wuille says.
Still, whereas some might shrug their shoulders and move on, Wuille remained hooked on bitcoin.
He told CoinDesk:
"At the time, when I discovered bitcoin, I didn't expect it would become my job or that I would spend every moment of my free time on it."
And he's used a nearly unbreakable focus to tune out the trash talk and continue lumbering along toward the future where cryptocurrency changes the world.
For him, SegWit was just one small step.
Zen Masters write code
But to get SegWit added to bitcoin was more of an uphill climb.
Introduced in 2015, the code was initially applauded by the community as big step for cryptocurrency, mainly in that it fixed a bug that prevented forward-looking projects from expanding the technology's capabilities. As a result of the change, ideas such as the Lightning Network and Schnorr signatures are possible to implement.
At the time, Wuille pitched the idea as a compromise that would appease both sides of bitcoin's scaling debate - one which wanted slow and steady scaling that wouldn't increase the size of the blockchain, and the other of which wanted more hasty on-chain scaling.
Still, SegWit turned out to be an unexpectedly controversial change.
To oversimplify, developers have generally sided with the "slow and steady" approach to code changes, whereas bitcoin companies and miners tended to want bigger and faster scaling, pointing to long transaction times and increasing transaction fees as deterrents that would keep new users from using the "digital currency."
As the debate between those two groups heated up, Wuille hardly chimed in on the debate raging around him. Mirroring a Zen Master who's undergone years of intense study to reach enlightenment, Wuille kept his head down.
And using the mantra "cypherpunks write code," Wuille endeared himself to the bitcoin community, which has respect for those that code up solutions to problems rather than attempt to achieve change by political or social means.
Bystanders to bitcoin's fiery debates have argued he's too "busy writing code" to get involved in all the drama.
Some go as far as to argue he knows bitcoin better than anyone. Dorier, for instance, says Wuille has a "near-complete understanding" of all of bitcoin's source code. And Bitcoin Core contributor Eric Lombrozo says Wuille "obsesses" over his coding work, albeit in a "peaceful" way.
Yet, on the phone, Wuille admits he hasn't been able to tune the debate out entirely.
"It's been heavy," Wuille told CoinDesk, sighing. "I've been in the middle of it for longer than it's been public."
The debate first entered the limelight in early 2015, when former Bitcoin Core maintainer Gavin Andresen published a series of blog posts advocating for an increase to the 1 MB block size parameter, a technical direction that many other developers shunned.
True to his reserved personality, though, Wuille wouldn't name any names or dive too deep into the details when asked for clarification.
He continues, sounding a little like a forlorn sage, "The whole block size debate started out among developers before certain people brought it to the public. But that was a long time ago."
And despite having opinions on the matter, in public he stayed composed - wading into the debate only to make short technical corrections.
In one fiery thread, for example, rather than point fingers or namecall, Wuille responded to one technical comment matter of factly: "This is wrong. The signatures are always needed when a node first processes a block, whether that is now or later."
Although, some developers wish he had expressed more of an opinion. Take Lombrozo, one of the group's more public members, who says he often ponders whether it would be better for Wuille and other shy coders to step up.
"I'd much rather people listened to people like Pieter," he says.
Social media channels are filled with misinformation and falsehoods, he argues, and developers like Wuille, who deeply understand how bitcoin works, could help to fill the gaps. That said, Lombrozo's not pushing too hard.
"It's just not his personality," he says. "He and developers like Van Der Laan shun the spotlight and the media in some ways. It's outside their comfort zone."
In this way, Purse.io founder and CEO Andrew Lee agrees. Even though he's personally tried to back alternative software efforts, he admires Wuille, calling him more "self-actualized" than the average person, meaning he knows what makes him happy in life - coding - and sticks with that.
Lee told CoinDesk:
"I think it's awesome that he has stayed out of it. Pieter knows where he wants to have an effect."
And that seems to be on other developers. Wuille has a history of passing on tips to newer coders, teaching the ways of the open-source bitcoin world.
Lombrozo notes that when he first attempted to get into bitcoin development, Wuille took him under his wing, teaching him about the tools and processes. (Lombrozo and Wuille would later buddy up to work on SegWit together).
"[Integrating SegWit] wouldn't have been possible without Pieter. He's super helpful to everyone in the space," Lee says.
Beyond all that, Dorier says Wuille has a sixth sense for bitcoin improvements.
"What's very impressive is that he's capable of knowing what's going to happen in the next year and focusing on the work for the shorter-term," he says.
And if Dorier's right, signature aggregation, a change championed by Wuille that mashes signature data together allowing more transaction data to fit into each block, could be one of the next bitcoin improvements.
Wuille revealed to CoinDesk that he's writing a more concrete bitcoin improvement proposal (BIP) for the code change.
And Dorier, who calls the upgrade "the next big step," guesses the change could be added to bitcoin in the next couple years. But why's Wuille doing all this? What makes the Zen Master spend all his time grinding away at bitcoin? As other developers and crypto-enthusiasts, he idealizes a future world with a fully functioning bitcoin.
"It might end up changing the world," Wuille says, adding:
"I think it can show how technology can remove the need for certain third parties and systemic risk that exists in the world."
But until then, and according to Wuille we're far from that, he'll keep tinkering away.
Because he believes, for all the animosity, the scaling debate hit a high point in 2017 because an ecosystem has blossomed around bitcoin, even though at a technical level it's not quite mature yet.
And that's the one thing many people fail to understand, he argues.
"Bitcoin's not ready for mainstream adoption. There are many unsolved problems," he says, pointing to privacy and scalability, among others.
And he still worries that it could all go down in ruin if there problems aren't solved.
"We need to get the incentives right so we don't just replace one banking system with another," he says.
But through it all, bitcoin's Zen Master leaves us with patient optimism like any good guru would:
"We'll get there in time."