As Tommy Robinson languished in a prison cell in rural Warwickshire this summer after a contempt of court conviction, the online campaign for his release spread rapidly across the globe.

Donald Trump Jr called it “reason #1776 for the original Brexit”, while a constellation of Twitter accounts – some identified as pro-Russian trolls by a US advocacy group – helped fuel outrage among the right.

The most vociferous online support came from a more unusual source, however. A Twitter user named @rebootbill posted a daily barrage of “#freetommy” tweets, racking up more than 4,700 within days.

The account was suspended by Twitter amid a crackdown on suspicious activity. It was not, in fact, a spambot or a Russian troll: it was run by a retired IT worker in the remote Canadian province of Prince Edward Island.

Bill Kays, 63, might not seem like the most obvious Robinson supporter. The devout Christian lives with his wife, Debbie, in Charlottetown, the island’s main city where he has spent most of his life. Kays describes himself on social media as a “critical thinking, anti-globalist, conservative libertarian”.

Kays told the Guardian he backed Robinson because he followed “everything that affects the global assault on free speech”. He said in an email: “Globalism is evil in its current form as everything we do is done under the threat of force.” He would not be drawn on whether he supported Robinson’s views on Islam.

Robinson has gone from being a fringe antagonist at far-right rallies to an international brand with supporters in high, and far-flung, places.

That brand will get another chance to exhibit on Sunday, when Robinson leads a “Brexit betrayal” rally in London.

The American right appears particularly seduced by Robinson. A Guardian investigation has found that over the past two years Robinson has received financial or political support from three US thinktanks. Between 2014 and 2016, these groups were given millions of dollars by some of the biggest names in conservative philanthropy.

Demonstrators hold banners supporting Tommy Robinson and the US president, Donald Trump, during a rally in London in July. Photograph: Yves Herman/Reuters

Robinson’s journey from convicted football thug to global cause célèbre began in 2014. The father-of-three, whose real name is Stephen Yaxley-Lennon, had all but retired from activism when he received a call from Ezra Levant, a conservative Canadian commentator. Levant wanted Robinson to be the European face of the Rebel Media rightwing website, which launched in 2015. Two years later, Robinson joined the network full-time, before leaving at the end of last year.

A series of terrorist attacks in Britain provided the backdrop for Robinson’s first months at the Rebel Media. He declared his country was at “war” within hours of the March 2017 Westminster Bridge attack, then after the Manchester Arena attack two months later, he branded Muslims “enemy combatants who want to kill you, maim you and destroy you”. Those two videos have been viewed almost 3m times on YouTube.

Robinson frequently complains of being smeared as a racist and a Nazi; he insists he doesn’t care about skin colour and that his objection is to Islamist political ideology rather than people.

Robinson was paid about £5,000 a month by the Rebel Media, a former colleague told the Guardian, in a role that was part-financed by a US tech billionaire whose clients include the supermarket chain Asda and the drug company AstraZeneca. Dr Robert Shillman, the founder of the Nasdaq-listed firm Cognex, has donated generously through his California-based foundation to various conservative and pro-Israel projects in the US, including a discredited website called Project Veritas, whose backers include Donald Trump.

As Robinson’s profile rose outside the UK, he became a “Frankenstein’s monster”, a former assistant told the Guardian. Lucy Brown, who was employed by the Rebel Media and then Robinson until May, said he pulled in large donations from people who felt dismayed at the mainstream media. “There’s definitely a cult forming around him,” she said.

In early 2017, Robinson turned his attention to grooming gangs. He filmed himself outside courts in Huddersfield and Leeds, hurling what a judge later described as “generically derogative” remarks about the defendants’ ethnicity and religion while claiming the child sexual abuse had been covered up.

The Rebel Media said it had raised £20,000 within hours of Robinson being arrested for filming outside a trial in Canterbury in May 2017. Almost a year later, Robinson was arrested outside Leeds crown court and found in contempt of court for a Facebook livestream about an ongoing child sexual exploitation trial. This time he was jailed. He was released on 1 August after the court of appeal ordered that he should be retried. The attorney general is deciding whether to proceed with a retrial.

The judge temporarily banned any reporting of Robinson’s arrest or imprisonment, but word of his arrest had already spread and an online campaign began. On 27 May, two days after the arrest, “#freetommy” became a “messaging priority” for an army of 600 Twitter accounts believed to be directly linked to the Russian government or closely aligned to its propaganda, according to research conducted for the Guardian by the US advocacy group Alliance for Securing Democracy.

Supporters clashed violently with police in a 15,000-strong protest that followed in Westminster, thought to be the biggest far-right demonstration in Britain for at least 40 years. The rally was funded and organised by the Philadelphia-based thinktank, the Middle East Forum.

Scrutiny of the MEF and other groups that have given Robinson financial or political support revealed that they in turn received almost $5m in funding from 2014-2016 from four US foundations.

Central to the MEF and other groups that have given Robinson financial or political support is Nina Rosenwald, the co-chair of American Securities Management who in 2012 was dubbed by the Nation website as “the sugar mama of anti-Muslim hate”. Rosenwald is the president and founder of the Gatestone Institute, which over the past two years has published a string of pro-Robinson articles online.

Rosenwald, who is an MEF board member, gave $2.9m between 2014 and 2016 to three groups that subsequently helped fund or champion Robinson, including Gatestone.

Tommy Robinson leaves Onley jail, near Rugby, after the court of appeal ordered he should be retried. Photograph: Joe Giddens/PA

Another smaller donor to Gatestone was the family of Robert Mercer, the New York hedge fund magnate who helped bankroll Trump’s campaign for the US presidency. Mercer’s family foundation donated $250,000 between 2014 and 2016 to the influential thinktank.

Money was also donated by a foundation of Richard Mellon Scaife, a deceased Pittsburgh billionaire who helped fuel the impeachment of President Bill Clinton in 1998 and has been described as one of the most generous donors to conservative causes in US history.

Between 2014 and 2016 his foundation donated $575,000 to the David Horowitz Freedom Center, which styles itself as a “school for political warfare” against the “fifth column” and the “enemy within”, and employs Robert Spencer, an anti-Islam polemicist barred from entering the UK. The DHFC has published a series of articles in defence of Robinson.

Another $875,000 was gifted to the MEF and the DHFC by the Milwaukee-based Lynde and Harry Bradley Foundation, which honours the legacy of two late industrialists and is an established backer of US conservative causes.

Robinson says much of his funding comes from individual supporters. He has claimed to have received “a few hundred thousand pounds” in donations to his website since May, while the Guardian has tracked nearly £8,000 in anonymous bitcoin payments to his account in the past four months – including a £4,756 transaction when Robinson was in prison, three days before the Westminster protest.

An analysis of Robinson’s Twitter support underscores its global scale. Of the 2.2m “#freetommy” tweets between May and October, 46% came from the US, compared with only 31% from the UK, according to the London-based Institute for Strategic Dialogue. The most-shared links were to rightwing outlets including the Rebel Media, InfoWars and the German conspiracy site Philosophia Perennis.

Robinson, addressing 2,000 supporters on a MEF-funded stage outside the Old Bailey in October, complained he was being silenced by the establishment. The media, he said, were “the enemy of the people”, as his supporters booed and chanted “U-S-A! U-S-A!”. He addressed Republican congressmen and women in Washington DC via video link in early November and has been considering a speaking tour of Australia.

His voice has never been louder.

Additional reporting by Carmen Aguilar

What they said

The Guardian contacted people named in this article for their response. Robinson, Shillman, the Mercers, the Scaife Foundation, the Lynde and Harry Bradley Foundation did not respond to detailed requests for comment.

MEF president, Daniel Pipes, wrote in an email:

“I am known for saying that radical Islam is the problem and moderate Islam is the solution. That, obviously, means I and MEF are not anti-Islam nor part of an anti-Islamic network. Indeed, MEF supports employs, and collaborates with Muslims in the fight against Islamism.

DHFC co-founder David Horowitz wrote in an email:

“Tommy Robinson is a courageous Englishman who has risked his life to expose the rape epidemic of young girls conducted by Muslim gangs and covered up by your shameful government.

“We are against the rape of young girls that is epidemic in England; we are against the disgusting efforts of the British government to protect the rapists, we support Tommy Robinson’s campaign to expose the rapists and rally the British public to stop them. That’s why we invited him to our restoration weekend.”

Nina Rosenwald and the Gatestone Institute have strongly denied they are anti-Islam

In a 5,000-word article in May, the institute said “far from being anti-Muslim” it was “pro-Muslim” and said it did not want to see “Muslims deprived of freedom of speech, flogged or stoned to death for supposed adultery”. It added that it was committed to educating the public about Sharia law, a branch of Islam, which it described as “incompatible with liberal democracy”.