He fit in as well as anyone did at our Los Angeles studio, a place full of ambitious misfits with an unusual gift. They knew how to make web videos people wanted to watch.

His real name was Anthime Joseph Gionet, though he preferred others. His value to BuzzFeed was clear: He’d do anything for the Vine, the short video platform that had a brief cultural moment before being crushed by Instagram and Snapchat in 2017.

Once, he poured a gallon of milk on his face and a clip of it drew millions of views, back when mostly harmless stunts amused millions of American viewers on the platform.

He was, in that way, a natural for BuzzFeed when he arrived in the spring of 2015, where I was editor in chief, overseeing the website. Mr. Gionet was hired to run the Vine account for our video operation, and his job mostly consisted of editing down to six seconds the silly, fun videos his colleagues produced. Within months, he took over a BuzzFeed Twitter account, too, drawing on his same intuition for what kind of video people would share.

We were better than anyone in those days at making things for social media, mostly lists and quizzes and short videos, but also occasionally spectacular live streams, most famously the one where two of my colleagues exploded a watermelon, one rubber band at a time.

And so the language I heard from Mr. Gionet, now 33, on his livestream last Wednesday was familiar. “We’ve got over 10,000 people live, watching, let’s go!” he said excitedly. “Hit that follow button — I appreciate you guys.”

Mr. Gionet was standing inside the trashed office of Senator Jeff Merkley of Oregon, streaming from one of the few platforms yet to ban him, alongside other Trump loyalists who played with the telephone receiver and draped themselves over the furniture. It seemed an apt conclusion to a recent career arc that some might see as trolling or internet pranks, but is probably best described as performative violence.

After I saw Mr. Gionet, I called up some of my old colleagues, who recalled him with a mixture of perplexity and repulsion. He was sensitive and almost desperate to be liked, they said, once getting extremely upset when someone made fun of his thick mustache and blond mullet. Two of his closest friends at the office at the time had different ethnic backgrounds and gender identities than he did, and they sometimes bonded over a sense of being outsiders. One of those friends remembered him as a sad character who didn’t really express political views beyond the broadly bro-ey and insensitive culture of Vine, and who confided that he was haunted by a lonely childhood in Alaska. He seemed, three of them said, to be missing something — to be hollow inside.

As the 2016 election took hold, he started to flirt with a political persona. He first put a Bernie Sanders portrait on his desk, two former colleagues said. Then, he moved on to wearing MAGA hats around the office, which raised eyebrows among his more progressive, if fairly apolitical, co-workers, though that was when some people still imagined the far right could be “ironic.”

When he left BuzzFeed later that year to work as the “tour manager” for Milo Yiannopoulos, a darling of the racist and anti-Semitic “alt-right,” colleagues were momentarily shocked. Then, they scrolled through Mr. Gionet’s Twitter account, where his increasingly vile statements were getting him retweets from far-right figures, and realized that they shouldn’t have been.

Still, it’s not clear what Mr. Gionet actually believes, if anything. And really, I’m not sure I care.

This isn’t a sympathetic profile of a young man gone wrong. I can’t muster much pity for a guy who, before he was attacking his Capitol, spent his time shooting some kind of bottled irritant (he called it “content spray”) into the eyes of innocent people for YouTube views and shouting at store clerks who asked him to wear a mask.

To me, this story is about something different, a sort of social media power that we helped sharpen at BuzzFeed that can exert an almost irresistible gravitational pull.

If you haven’t had the experience of posting something on social media that goes truly viral, you may not understand its profound emotional attraction. You’re suddenly the center of a digital universe, getting more attention from more people than you ever have. The rush of affirmation can be giddy, and addictive. And if you have little else to hold on to, you can lose yourself to it.

Even as we sought to make our work spread at BuzzFeed, we faced constraints — by truth in our news division, by hewing to a broadly positive set of values on our entertainment side. But Mr. Gionet ultimately broke loose of those boundaries, seeming to follow the signals he found on social media without any scruple. The only through line was his desire to build an audience. He was boosting Bernie Sanders before he was chanting anti-Semitic slogans in Charlottesville, Va., then temporarily recanting those extreme views and later committing violent crimes to get views on YouTube. He built an audience among coronavirus deniers and then, when he apparently contracted the disease, posted the screenshot of his own positive test to Instagram with a tearful emoji. A few weeks later, he joined the pro-Trump uprising in the Capitol.

“His politics have been guided by platform metrics,” reflected Andrew Gauthier, who was a top video producer at BuzzFeed and later worked for Joseph R. Biden Jr.’s presidential campaign. “You always think that evil is going to come from movie villain evil, and then you’re like — oh no, evil can just start with bad jokes and nihilistic behavior that is fueled by positive reinforcement on various platforms.”

And so Mr. Gionet’s story isn’t quite the familiar one of a lonely young man in his bedroom falling down a rabbit hole of videos that poison his worldview. It’s the story of a man being rewarded for being a violent white nationalist, and getting the attention and affirmation that he’s apparently desperate for.

We spent a lot of time at BuzzFeed thinking about how to optimize our content for an online audience; he optimized himself.

When he was arrested in Scottsdale, Ariz., last month for spraying mace into the eyes of a bouncer, an officer reported that Mr. Gionet “informed me that he was a ‘influencer’ and had a large following on social media,” according to a police report. He was released on his own recognizance, a Scottsdale police spokesman said, and is awaiting trial. Nonetheless, in the Capitol, he yelled “A.C.A.F.” — All Cops Are Friends (though the original meaning of the acronym is less friendly).

His story leaves me wondering what share of blame those of us who pioneered the use of social media to deliver information deserve at this moment. Did we, along with the creators of those platforms, help open Pandora’s box?

I didn’t work directly with Mr. Gionet. But in 2012, I did hire a writer named Benny Johnson who was cultivating a voice that blended social media savvy and right-wing politics. I thought, wrongly, of his politics at the time as just conservative. And I imagined him thriving, as conservative writers have done for generations in mainstream newsrooms, where they shared their colleagues’ interest in finding shared facts.

I was slow to realize that his interests weren’t journalistic, or even ideological, as much as they were aesthetic, thrilled by the imagery of raw power. In the tradition of authoritarian propagandists, he was awed by neoclassical buildings, guns and, later, Donald Trump’s crowds. And, after we fired him for plagiarism in 2014, he went on to lead the content arm of Mr. Trump’s youth wing, Turning Point USA, and host a show on Newsmax. Last week, he was cheerleading attempts to overturn the election (though he pulled back when the violence began and later blamed leftists for it). He’s also selling his skills in the “viral political storytelling” that we worked together on at BuzzFeed to a generation of new right-wing figures like Representative Lauren Boebert, who has won attention for vowing to bring her handgun to work in Congress. (Neither Mr. Gionet nor Mr. Johnson responded to email inquiries.)

While we were refining the new practice of social media at BuzzFeed, we were slow to realize that the far right was watching closely and eventually imitating us. Jonah Peretti, who founded The Huffington Post as well as BuzzFeed, was surprised when Steve Bannon, who ran Breitbart, recalled to a writer that he’d borrowed elements of his strategy from Mr. Peretti in the run-up to the 2016 election. Mr. Bannon told me before that election, in an interview in Trump Tower, that he was surprised we hadn’t turned BuzzFeed to pure Bernie Sanders boosterism, as Breitbart did for Donald Trump. He noted, probably correctly, that the traffic for a pro-Sanders propaganda outlet would have greatly exceeded what we got for fair coverage of the Democratic primary.

“Some of the innovative things we did early on, in understanding social media and digital media, have been taken up by alt-right groups, racist groups, MAGA groups,” my old boss, Mr. Peretti, told me in an interview last week. But Mr. Peretti, an eternal optimist, noted that some of the same social mechanisms that Mr. Gionet exploited were also crucial to the sweeping progressive social movements of the last few years, from Black Lives Matter to #MeToo. “The story’s not done and there’s an opportunity to fight for a good internet,” he said. (Disclosure: I don’t cover BuzzFeed extensively in this column, beyond leaning on what I learned during my time there, and The Times has required that I not do so until I divest my stock options in the company.)

I’m already hearing what seem to be two competing explanations of what happened in Washington last week: that the overwhelmingly white, sometimes overtly racist, mob embodied old, deep unexpurgated American evil; or that social media reshaped some Americans’ blank slate identities into something radical.

But Mr. Gionet’s story shows how those explanations don’t really conflict. A man his colleagues saw as empty and driftless turned his identity into a kind of a mirror of that old American evil, and has become what many Americans told him they wanted him to be.

At one point in Mr. Gionet’s livestream during the siege of the Capitol, an unseen voice off camera warns that President Trump “would be very upset” with the antics of the rioters.

“No, he’ll be happy,” Mr. Gionet responded. “We’re fighting for Trump.”