It was known as F.O.S. — or Friends of Stone — and while its members shifted over time, they were a motley cast of characters.

There were “Stop the Steal” organizers, right-wing influencers, Florida state legislative aides and more than one failed candidate loyal to former President Donald J. Trump. One participant ran a website that promoted disinformation about the Capitol attack. Another was an officer in the Army Reserve allied with Michael T. Flynn, Mr. Trump’s former national security adviser.

At least three members of the group chat are now facing charges in connection with the riot at the Capitol in January 2021. They include Owen Shroyer, the right-hand man of the conspiracy theorist Alex Jones; Enrique Tarrio, the onetime chairman of the Proud Boys; and Stewart Rhodes, the leader of the Oath Keepers militia.

But the focus of the chat was always the man whose photo topped its home page: Roger J. Stone Jr., a longtime political operative and adviser to Mr. Trump.

While little is known about what was said on the chat, the membership list of Friends of Stone, provided to The New York Times by one of its participants, offers a kind of road map to Mr. Stone’s associations, showing their scope and nature in the critical period after the 2020 election. During that time, Mr. Stone was involved with a strikingly wide array of people who participated in efforts to challenge the vote count and keep Mr. Trump in the White House.

Some of the 47 people on the list are identified only by nicknames or initials, and Mr. Stone had pre-existing political ties with many of them. Still, as prosecutors deepen their inquiry into the storming of Capitol, the list suggests that Mr. Stone had the means to be in private contact with key players in the events of Jan. 6 — political organizers, far-right extremists and influential media figures who subsequently played down the attack.

Reached by email, Mr. Stone said that he did not control who was admitted to the group chat and noted that Stop the Steal activities were protected by the First Amendment.

“There is no story,” he wrote. “Just harassment.”

While the origins of the group chat remain somewhat obscure, Friends of Stone has existed since at least 2019, when Mr. Stone was indicted in connection with the Russia investigation by the special counsel Robert S. Mueller III, said one of its participants, Pete Santilli, a veteran right-wing radio host. According to Mr. Santilli, the group chat — hosted on the encrypted app Signal — was a kind of safe space where pro-Stone figures in politics and media, many of whom were banned from social media, could get together and trade links and stories about their mutual friend.

“The primary reason for the chat was to have a place for supporters to share stuff,” Mr. Santilli said. “You drop a link and everyone shares it on their nontraditional channels.”

But after Mr. Trump’s defeat, Friends of Stone seemed to assume another purpose as Mr. Stone found himself in the middle of the accelerating Stop the Steal movement devised to challenge the results of the election. The Washington Post, citing footage from a Danish documentary film crew that was following Mr. Stone, said that in early November 2020, he asked his aides to direct those involved in the effort to monitor the chat for developments.

In recent weeks, the Justice Department has expanded its investigation of the riot from those who physically attacked the Capitol to those who were not at the building but may have helped to shape or guide the violence. Investigators appear to be interested in finding any links between organizers who planned pro-Trump rallies at the Capitol that day and right-wing militants who took part in the assault.

The group chat’s membership list includes several people who fit that description.

Named on the list are activists like Marsha Lessard and Christina Skaggs, leaders of a group called the Virginia Freedom Keepers who helped to organize an anti-vaccine rally scheduled for the east side of the Capitol on Jan. 6. Ms. Lessard and Ms. Skaggs worked with another anti-vaccine activist, Ty Bollinger, who was also on the list.

Members of the group were among those who took part in a conference call on Dec. 30, 2020, when a social media expert who formerly worked for Mr. Stone urged his listeners to “descend on the Capitol” one week later, promising that Joseph R. Biden Jr. “will never be in that White House.”

Ms. Lessard, Ms. Skaggs and Mr. Bollinger did not return phone calls seeking comment.

Ali Alexander, one of the most prominent Stop the Steal organizers who planned his own event at the Capitol that day, was on the list as well. His lawyer did not return a phone call seeking comment.

In the days leading up to Jan. 6, Mr. Stone was scheduled to speak at both Mr. Alexander’s event and the rally hosted by Ms. Lessard, Ms. Skaggs and others, including Bianca Gracia, the leader of a group called Latinos for Trump, according to permits and event fliers. Mr. Stone never spoke at those events, however, and hurried out of Washington even as the police were still securing the Capitol, according to the film footage cited by The Post.

Mr. Stone’s connections to Mr. Rhodes and the Oath Keepers were based, at least in part, on the fact that the militia group provided security for him on Jan. 5 and Jan. 6. The Oath Keepers also protected Mr. Alexander and his entourage on Jan. 6 and served as security at the events hosted by Ms. Skaggs, Ms. Lessard and Ms. Gracia, court papers say.

At least one of Mr. Stone’s Oath Keeper bodyguards, Joshua James, has pleaded guilty to seditious conspiracy charges in the Capitol attack and is cooperating with the government’s inquiry. Kellye SoRelle, a lawyer for the Oath Keepers, was part of the Friends of Stone chat as well and is also said to be cooperating with prosecutors in the riot investigation.

Mr. Stone, a Florida resident, has long maintained close ties to the Proud Boys, especially to Mr. Tarrio, who lived in Miami before his arrest. Members of the Proud Boys have acted as bodyguards for Mr. Stone and have served as some of his most vocal supporters.

In 2019, after Mr. Stone was indicted by Mr. Mueller on charges including obstruction and witness tampering, Mr. Tarrio responded by wearing a T-shirt reading “Roger Stone Did Nothing Wrong” at one of Mr. Trump’s political rallies. At one point, Mr. Tarrio’s personal cellphone had a message recorded by Mr. Stone.

Nayib Hassan, Mr. Tarrio’s lawyer, declined to comment on his client’s role in the chat.

During his prosecution, Mr. Stone posted an image on social media of the federal judge in his case, Amy Berman Jackson, with cross hairs next to her head. When questioned in court about the image, he acknowledged that he had been sent a series of photos by Mr. Tarrio and two other Florida Proud Boys whose names appear on the Friends of Stone membership list: Jacobs Engels and Tyler Ziolkowski.

Mr. Engels was with Mr. Stone in Washington on Jan. 5 and Jan. 6. He initially agreed to talk about the group chat but then did not return a phone call seeking comment.

Another person who appeared on the Friends of Stone list — under the name “Ivan” — was Ivan Raiklin, an Army Reserve lieutenant colonel who promoted a plan after the election to pressure Vice President Mike Pence not to certify electors from several disputed swing states. This plan, which Mr. Raiklin called the “Pence Card,” was ultimately taken up by Mr. Trump and some of his legal advisers, like the lawyer John Eastman.

Mr. Raiklin, who did not return phone calls seeking comment, was at the Capitol on Jan. 6, but showed no sign of entering the building. Closely aligned with Mr. Flynn, he has continued to question the results of the 2020 vote, appearing at so-called election integrity events and arguing that Mr. Trump was set up by members of the “deep state.”

While the government has gathered thousands of pages of private messages in its vast investigation of the Capitol attack, it remains unclear if prosecutors have gotten access to the Friends of Stone group chat. Along with the membership list, The Times was given images of a few snippets of conversations to verify the chat’s authenticity.

In one of them, Ms. Skaggs told the group that she had just spoken with the pro-Trump lawyer L. Lin Wood, who took part in the effort to overturn the election. Ms. Skaggs’s message, which does not bear a date, said Mr. Wood was claiming that the Insurrection Act — a form of martial law — had been invoked the night before.

Responding to her message, Mr. Rhodes, who had repeatedly urged Mr. Trump to use the Insurrection Act to stay in power, answered incredulously.

“I’ll believe it when I see it,” he wrote, dismissing the account with an obscenity.