For $150, Brad Holiday’s customers could purchase and download a package of dating tips and tricks he called his “Attraction Accelerator.” The batch of files featured advice from Mr. Holiday, a self-styled Manhattan dating coach, about things like the best facial serums and pickup lines, and his thoughts on the viciousness of the opposite sex.

But tucked between videos denigrating women and reviews of height-boosting shoes were other guides: how to defeat Communists, expose what he claimed were government pedophilia cabals, and properly wield a Glock.

On Jan. 20, F.B.I. agents arrested the man, whose real name is Samuel Fisher, outside his apartment on the Upper East Side in connection with his involvement in the Jan. 6 attack on the Capitol. Stashed in his Chevrolet Tahoe, parked on East 88th Street, investigators found a shotgun, machetes and more than a thousand rounds of ammunition, according to court records.

Like many of the roughly 175 people arrested after the riot, Mr. Fisher left a trail of social media posts about his exploits. “People died,” but it was great, Mr. Fisher wrote online after the attack, according to court records. “Seeing cops literally run … was the coolest thing ive ever seen in my life.”

After his arrest, Mr. Fisher was ordered held without bail, according to Tamara Giwa, a federal public defender appointed to his case. Court records show he is to be moved to Washington to face charges of disorderly conduct and unlawful entry.

He had not entered a plea as of Thursday, and Ms. Giwa did not respond to subsequent calls and messages seeking comment about the case.

The composition of the mob that stormed the Capitol last month has come into sharper focus as arrests linked to the incident mount. In New York, the people charged include an accountant, a sanitation worker and a retired firefighter.

Among them were a handful of men like Mr. Fisher, whose large online footprint suggests a fierce devotion to a hypermasculine ethos of chauvinism, grievance and misogyny. His scores of videos, treatises and posts, spread across web pages and social media profiles, reflect a worldview that festers on the far-right fringe.

This ideology’s mostly male adherents — including the far-right group the Proud Boys, who have become a chief focus of the F.B.I.’s investigation into the Capitol attack — appear to have united in part over their shared support for former President Donald J. Trump.

“Tomorrow, Trump and We The People will be betrayed again by every so called representative who said they’d fight for us,” Mr. Fisher wrote on his website, bradholiday.com, the day of the riot.

In a photograph posted to one of Mr. Fisher’s Facebook pages and sent to the F.B.I. by an unnamed informant, Mr. Fisher poses grinning before a Trump flag, a pistol in his hand, a rifle and a shotgun behind him.

“Can’t wait to bring a liberal back to this freedom palace,” the caption reads, apparently referring to his home.

Sitting before a backdrop of a Trump flag in one of his most recent videos about a week after the riot, Mr. Fisher veers wildly from railing against the Left to assailing women.

“Is Satanism a good thing? Should we conjure demons to get our goals met like the Left does?” he said, adding a vulgarity. “Are women trustworthy in 2020? You tell me; I’ll tell you no.”

Of the more than half-dozen friends and clients of Mr. Fisher interviewed for this article, all spoke on the condition of anonymity for fear of being harassed by people who share his views.

As Brad Holiday, Mr. Fisher, a former guitar teacher, filled websites with reams of video tutorials. His online presence in part earned him invitations to speak at men’s empowerment seminars.

In 2017, Vince Kelvin, a well-known pickup instructor, invited the man he knew as Brad Holiday to speak at his dating symposium in Manhattan. But after hearing Mr. Fisher’s beliefs, Mr. Kelvin said, he swiftly terminated the relationship.

“My experience was right away, what is this guy talking about?” Mr. Kelvin said in an interview.

Mr. Fisher’s online files are filled with dubious practices, including tutorials on how to rejoin online dating sites after being banned for harassment — something he says he has experienced personally — and a website he appears to have created solely to feature screenshots of nasty text exchanges with women.

He also offered a glimpse of his own personal struggles. In videos no longer online, several of the people said, Mr. Fisher described overcoming substance abuse and a period of homelessness. He would often take floundering young men under his wing and teach them “how to be a man” at no charge, according to a former roommate.

Some experts said men like Mr. Fisher were particularly attracted to Mr. Trump because they see him as emblematic of a certain kind of masculinity.

“The men that are in these movements themselves try to enact that kind of masculinity, and because Trump enacts it they are drawn to him,” said Ronald F. Levant, co-author of the book “The Tough Standard: The Hard Truths About Masculinity and Violence.” “He models it. He gives them permission.”

Mr. Fisher grew up in New Jersey and told people he was estranged from his family. The divide grew sharper, according to one friend, as Mr. Fisher began to burrow deeply into online conspiracy theories, including QAnon.

Mr. Fisher was born Jewish and in videos said he turned to Christ. He shared anti-Semitic articles and videos accusing Jews of cannibalism.

Growing up, Mr. Fisher “was bullied, he always thought that everybody was out to get him, including women,” said a man whom Mr. Fisher mentored and who credited his advice with helping quell panic attacks.

About three years ago, Mr. Fisher posted online about his rage at being cheated on by a woman with whom he has a child, according to people with knowledge of the posts. He told friends he wished he could see more of his young daughter, who lived with her mother in New Jersey.

Around then, his dating tips began to spiral into aggression and his musings began to drift toward conspiracy theories, friends said.

Around the election, Mr. Fisher headed to Baldwinsville, N.Y., just northwest of Syracuse, where he took up residence on a former client’s couch, according to someone with knowledge of the situation. But the relationship became strained when packages began arriving: first one tactical vest, then another. Then two machetes.

After his arrest, agents left behind a document detailing what was seized from his Chevy, according to reports; among the clips of bullets are two tactical vests and two machetes. According to the criminal complaint, Mr. Fisher brought some of these items, including a firearm, with him to Washington on Jan. 6.

“And if it kicks off,” he wrote on Facebook that day, according to court records, “I got a Vest and My Rifle.”

Sean Piccoli contributed reporting and Alain Delaquérière contributed research.