Over the past several months, author and conspiracy theorist Jerome Corsi has emerged as one of special counsel Robert S. Mueller III’s most vexing witnesses in his probe of Russian interference in the 2016 campaign.

Corsi — perhaps best known for promoting the false idea that former president Barack Obama was not born in the United States — has released internal special counsel documents, fulminated against alleged plea-deal offers and published a hastily written e-book outlining his account of interactions with his onetime ally, the longtime Trump adviser Roger Stone, a subject of intense scrutiny in Mueller’s probe.

At the same time, Corsi says, he has been collecting what he describes as $15,000-a-month payments from Infowars, a website that has attacked the special counsel investigation as a deep-state conspiracy designed to topple President Trump.

An attorney for Infowars confirmed that these payments continued for the past six months as severance since Corsi lost his post as the website’s Washington bureau chief — a job that Stone helped arrange, according to both Corsi and Stone.

The revelation of Corsi’s arrangement with Infowars offers new context to the now-frayed relationship between Corsi and Stone, and how the on-again, off-again alliance between two of America’s foremost conspiracy theorists has drawn the attention of Mueller’s investigators.

Stone has said that research conducted by Corsi informed his predictions in 2016 that WikiLeaks would publish material damaging to Hillary Clinton’s presidential campaign. Mueller has charged Russian intelligence officers with hacking Democratic emails and providing them to WikiLeaks. For months, he has been investigating whether Stone was working in coordination with the group, which Stone adamantly denies.

As part of the investigation into Stone, Mueller’s prosecutors have interviewed a number of his associates and zeroed in on his relationship with Corsi, including emails between the two men in which Corsi indicated he had insight into WikiLeaks’ plans, according to Corsi.

On Thursday, Corsi’s stepson, Andrew Stettner, appeared before a grand jury hearing evidence in the case for about an hour. Afterward, his attorney Larry Klayman told reporters that Stettner had been questioned about his handling of Corsi’s computers.

Investigators have also asked questions about Corsi’s payments from Infowars, according to a person familiar with the special counsel investigation. Mueller’s team appears to be exploring whether the payments were made to ensure that Corsi would offer investigators a version of events favorable to Stone, the person said.

Corsi said in an interview that he does not remember being asked by Mueller’s investigators about the payments. But he added that his brain was “mush” after 40 hours of questioning over several days and that he may have forgotten.

“It’s really pretty far-fetched,” Corsi said of the notion he was paid to keep quiet. “I’m the guy who has talked the most. I haven’t been hushed by anything.”

Stone, who has said he has not been contacted by the special counsel, called the suggestion that he helped Corsi get work to silence him “both ridiculous and false.”

The extent of the special counsel’s interest in Corsi’s arrangement with the website is unclear. An attorney for Infowars said the site has not received any request for information from Mueller. A spokesman for the special counsel’s office declined to comment.

After The Washington Post made inquiries about the payments last week, Corsi said he learned from Alex Jones’s father, David, that the payments would stop, according to a legal complaint Corsi filed this week against The Post.

An Infowars attorney disputed that, saying that Corsi was fired in June and was paid the remainder of a one-year contract that ended this month. His Infowars pay had already been scheduled to end this month, the attorney said.

“Any claim that he stopped receiving those payments because of The Washington Post asking questions does not appear to be supported by any facts I know of,” Infowars attorney Marc Randazza said.

In a letter to Corsi dated Jan. 18 — a day after The Post first interviewed him — David Jones wrote that he had agreed to pay the remainder of Corsi’s contract after he was terminated in June “because of our history and contract considerations.”

“As I discussed with you some time ago I cannot indefinitely pay your salary continuation,” Jones wrote in the letter, which was posted online by Stone. Jones added that he would terminate the contract as of Jan. 31.

In an interview last week with The Post, Corsi offered two explanations for the payments that have drawn the interest of prosecutors. Initially, he described them as consulting fees related to the “exploratory” phase of a “fake news” project that he and David Jones — a former dentist who is the director of human resources for Infowars — were considering launching. Corsi said that the payments were “not directly related to Infowars.”

Corsi later described the payments as severance after he left his post of Washington bureau chief for Infowars over the summer, a position that Stone helped him secure in early 2017 after Trump took office.

Stone, Corsi and Alex Jones all said that the Infowars job and the payments Corsi received after leaving are not related to Corsi’s role in the Mueller probe.

“I assisted him because he was constantly whining about being broke,” Stone said in an interview.

Corsi declined to comment on Stone’s characterization of his finances.

In an Infowars column published Jan. 18, Jones wrote that “hiring Corsi had nothing whatsoever to do with WikiLeaks or any kind of ‘hush money’ operation, which is an absurd claim.”

He noted that Corsi was hired almost two years before being interviewed in the special counsel’s investigation and he described payments to Corsi as “routine six months severance pay” following Corsi’s departure from Infowars in June.

Corsi filed a complaint Monday against The Post; its owner, Jeffrey P. Bezos; and Manuel Roig-Franzia, one of the authors of this article, who had interviewed Corsi about his relationship with the website. The complaint amended a previously filed lawsuit that names as defendants Mueller, the FBI, the National Security Agency and the Central Intelligence Agency. It seeks $1.6 billion in damages, including at least half of that from Bezos.

In the lawsuit, Corsi claimed The Post’s reporting amounted to “tortious interference” with his business relationship with Infowars.

A Post spokeswoman declined to comment on the lawsuit.

Corsi and Stone, who have become intertwined in the Mueller probe, were first brought together by Donald Trump.

Stone has previously told The Post that he first became aware of the conspiracy theorist and conservative writer when Trump posed a question to him in 2011: “Who is this guy, Jerome Corsi?”

When Stone asked Trump why he wanted to know about Corsi, Trump responded: “I’ve been talking to him.”

Corsi had recently published a book titled “Where’s the Birth Certificate: The Case That Barack Obama Is Not Eligible to Be President.” Trump became the most ardent public proponent of Corsi’s theory, staging splashy public appearances to taunt Obama to provide more proof about his birth.

Both men were ardent supporters of Trump’s 2016 campaign and collaborated in hopes of getting the New York developer elected to the nation’s highest office.

During the campaign, Stone has said he hired Corsi to conduct research about the Clintons and the Democrats. Later, they would offer conflicting accounts of their work together.

A key moment came on July 22, 2016, when WikiLeaks published tens of thousands of internal emails from the Democratic National Committee. The cache revealed tensions within the party during the primary contest between Sen. Bernie Sanders (I-Vt.) and Hillary Clinton. The revelations resulted in the resignation of the party chairwoman.

There was widespread speculation about what else WikiLeaks might have and when the group would release it. Stone saw an opportunity.

On July 25, 2016, Stone emailed Corsi and asked him to try to make contact with WikiLeaks founder Julian Assange and get copies of hacked emails in his possession, according to a draft court document drawn up by Mueller’s investigators. In November, Corsi publicly released the document, which he said he been provided by the special counsel’s office during failed plea negotiations.

Stone has said he was reacting to claims Assange had made on television about having damaging material about Clinton, characterizing his interest in the potential disclosures as no different from that of journalists and political operatives at the time.

When investigators first asked Corsi about the email, he claimed that he told Stone that trying to reach Assange could result in an investigation and they should wait for WikiLeaks to release material publicly, according to the draft court filing.

But, according to the filing, Corsi actually forwarded Stone’s email to a London-based associate and later wrote Stone an email about WikiLeaks’ plans. “Word is friend in embassy plans 2 more dumps,” Corsi wrote Stone on Aug. 2, 2016, according to the draft filing.

Corsi has said he surmised what WikiLeaks would do based on public reporting at the time but did not make contact with Assange.

That same month, Corsi has said in interviews, he told Stone that he believed — based on his own analysis of the DNC emails released in July — that WikiLeaks had hacked emails from Clinton campaign chairman John Podesta.

He has said he believes his tip is why Stone tweeted “it will soon [be] the Podesta’s time in the barrel” on Aug. 21, 2016 — about six weeks before WikiLeaks began releasing Podesta’s emails.

Stone has denied that Corsi told him WikiLeaks had Podesta’s emails and said his tweet was based on unrelated research Corsi had provided him about John and his brother Tony Podesta’s financial ties to Russia.

Stone’s tweet was one of several statements he made before the election suggesting he was in contact with Assange and had advance knowledge of WikiLeaks’s plans to release hacked emails — comments now under scrutiny by the special counsel.

Since the election, Stone has insisted he had no contact with Assange and did not know what the group planned. He has denied all wrongdoing and said he has been unfairly targeted by Mueller.

Stone and Corsi’s relationship continued after Trump’s election victory.

Stone suggested that they both go to work for Infowars, Corsi said in an interview. Randazza, the Infowars attorney, told The Post that Corsi was one of about 15 people whom Stone recommended to Jones as possible chiefs of the new Washington bureau for the conspiracy site. Randazza said Jones believed Corsi was the best and most experienced of the list.

Stone became a co-host and frequent commentator on the site, a position he maintains to this day. Corsi got the bureau chief job in Washington.

Corsi, who has a securities license, said he also took an interest in the business operations of the site, approached Alex Jones about financing options for Infowars.

“Alex was not wanting investors,” Corsi said in an interview. “We had some differences. Those differences, over time I think, led to our parting of the ways.”

In the column published by Infowars, Alex Jones wrote that Corsi’s employment with the company ended in June after Corsi’s “failure to adequately establish a Washington bureau, his failure to maintain White House press credentials and his generally poor work performance.”

Corsi said in an interview that he could not remember if he “was fired or I quit.”

“We just kind of mutually — without talking about it — decided I wasn’t working there anymore,” Corsi said.

Three months after his split with Infowars, Corsi was subpoenaed in the Mueller probe. At the time, Corsi’s attorney said that he would cooperate fully with the investigation.

It wasn’t long before his role as a witness caused friction with Stone and the two began attacking each other publicly. In November, Corsi asserted in interviews that Stone had urged him to come up with a cover story to explain the Podesta tweet by sending a research memo nine days after the tweet had been posted.

Stone has said that the memo was simply memorializing conversations they had had before the tweet and called Corsi’s claim “both categorically false and ludicrous — not to mention illogical.”

Corsi also said in November that he’d been cooperating with Mueller’s team but had decided to reject a plea deal proposed by prosecutors because it included a requirement that he admit to lying about his interactions with Stone.

From their respective corners of the Internet, the two conspiracy maestros have spent the months since then in verbal combat with Mueller and each other.

In his lawsuit, Corsi declared that Mueller and the media were in cahoots to set in motion a “legal coup d’etat” to either indict Trump or remove him from office. On Infowars last week, Stone and Alex Jones discussed a grand scheme by prosecutors and the media to arrest both of them, as well as Jones’s father, Trump and Vice President Pence, to install House Speaker Nancy Pelosi as president and Hillary Clinton as vice president. Stone then predicted that Pelosi would resign and Clinton would become president.

As their feuds with each other and with the special counsel’s office have deepened, both Corsi and Stone have taken to appealing to a higher power.

Corsi took to Twitter recently to accuse Mueller and the “Deep State” of trying to destroy him and his family.

“If I can hold a pen, I will not be silenced,” he tweeted. “In the end, God always wins.”

On Instagram, Stone declared that Corsi, a friend turned enemy, would suffer for not standing by him: “God will strike this liar down.”

Spencer S. Hsu contributed to this report.