Jim Dowson has been described as Britain's "most influential" far-right activist by UK anti-racism campaigners, having founded the nationalist group Britain First and in recent years been a central figure in Knights Templar International - a Christian militant group based in the UK.
Now the BBC, in collaboration with the Balkan Investigative Reporting Network, has seen evidence suggesting he is behind a network of Facebook pages with about 2.5 million followers.
You have probably never heard of Jim Dowson, which is how he prefers it.
He likes to fly under the radar and is not as well-known to most people as his close ally and fellow former British National Party activist Nick Griffin.
He made his name among far-right sympathisers on social media, where he was instrumental in founding anti-Islamic group Britain First.
That group, which he left in 2014, was banned from Facebook last month for repeatedly violating the social media giant's community standards. Its leaders were jailed for religious hate crimes earlier this year.
In 2015, Knights Templar International (KTI) - a militant Christian group that harks back to the age of the Christian Templars - emerged. Based in the UK, it has members around the world.
Mr Dowson's sister-in-law is registered as the official director of KTI's company in the UK, but it is Mr Dowson who from the get-go played the role of front man - appearing in videos promoting the group, making speeches and attending fundraising events.
He has been banned from one European country - Hungary - for being a national security threat.
KTI is Mr Dowson's "baby", says Matthew Collins from anti-racism group Hope Not Hate.
"It is the front group that he set up, [to defend] Christianity from these barbaric hordes of cultural Marxists, homosexuals, Muslims and any number of individuals or organisations that he doesn't like," he claims.
Despite the prominent part he plays, and the fact that he has, in past interviews, been referred to as KTI's director without him contradicting the information, Mr Dowson has told the BBC he has "no official position" within the group and is not a director.
Previously Mr Dowson has said that KTI is run by a council of nine people, and he follows their orders.
It is unclear how many KTI members there are, but in a January 2018 interview with a right-wing US radio station Republic Broadcasting Network, Mr Dowson said that KTI was "strongest in the UK. Outside of the UK - Poland, Hungary and then America. We are very strong in America, we have about 4,500-5,000 members."
The lowest price for KTI membership is £65, which means that if Mr Dowson's claims about the size of the group are correct they will have gathered hundreds of thousands of pounds in fees.
To see where some of the money could be going we travelled to Kosovo, where, 20 years ago, more than 10,000 people were killed in a conflict between Serb forces and ethnic Albanians.
Find out more
Simon Cox's investigation for BBC Radio 4, The Invisible Man of Britain's Far Right, is broadcast at 20:00 on Tuesday 1 May.
The Victoria Derbyshire programme is broadcast weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel.
The country remains a tinderbox of religious tensions, its fragile peace still having to be watched over by Nato troops decades after the conflict ended.
KTI has boasted of sending military equipment to Kosovo including ballistics vests and communications equipment, and posting pictures of some of the gear which it says is to combat what it calls "Islamist oppression".
In the Republic Broadcasting Network interview in January, Mr Dowson said he himself had recently taken "a huge consignment of bullet-proof vests and tactical equipment" there.
He has also appeared in a video urging people to donate money for the purchase of equipment, saying "they need practical things like night vision goggles, tactical vests, ration packs. They need all of these things to keep an eye on this because this will kick off at any moment."
He has previously said the Serbs did not need to be sent weapons as the region is awash with them already.
Responding to the BBC's claims, Mr Dowson told Victoria Derbyshire it was a "ludicrous assumption" to suggest that he was "stirring up tensions" in the area, adding it was important for people in the region to be given "protective vests".
He said he "rejects violence".
To help spread its message KTI has a website and Facebook page with almost 600,000 followers, which host videos posted from the UK and Eastern Europe.
It also has an online television channel, broadcasting videos filmed in Serbia.
The material on the channel is described by anti-far right campaigners as inflammatory in nature.
Films which are broadcast on it often talk of an impending war between Christians and Muslims, and denounce mass immigration and the "Islamification" of Europe.
The content on KTI's Facebook page is much more mainstream, with videos supporting British troops attracting a big audience.
However, campaigners say it is still a platform for extremism - when videos about Muslims are posted they attract thousands of comments - much of it hate speech. Facebook says it is now investigating this.
Mr Dowson told Wired magazine in February he "never was really that involved" with Knights Templar International or any of the sites it shares a server with.
However, it is clear from our investigation - in collaboration with the Balkan Investigative Reporting Network (Birn) - that Mr Dowson does wield significant influence online.
Andrej Petrovski, a social media analyst from Birn, has been analysing the links between Mr Dowson and a network of a dozen Facebook pages.
A lot of the content shared on the sites is made in Serbia, where Mr Dowson is a frequent visitor, but despite its origins most of it is in English and aimed at a UK audience.
Much of the material is not far right in nature, but mainstream content and it is hugely popular. Andrej Petrovski says that between them the pages have 2.5 million followers - more than the UK's Conservative and Labour parties combined.
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He said that the people consuming and sharing the material here in the UK include "200 people working for different UK councils".
"We found over 150 people working for the NHS, we found teachers, we found nurses, we found sitting MPs, sitting MEPs and literally all sorts of people," he added.
According to Andrej Petrovski's analysis, the dozen websites are linked as they are hosted on the same server, which he says means they are shared by the same person, group or company.
Some of the sites have had Google Ads, making money when people clicked on them.
A whistleblower who knows about Mr Dowson's operation has shown us evidence that these sites made over £100,000 in just an 18-month period.
The revenue generated then goes into an online financial wallet, which the whistleblower revealed feeds into a bank account for a company solely run by Mr Dowson. We do not know how long the account has been connected to the wallet.
Speaking to the BBC, Mr Dowson said the whistleblower does not exist.
He said he does not have any online "wallet".
He said he could not recall if he was the director of that company, and said "any company I'm in control of has never received £100,000".
'Advising' a new generation
We have also been told that Mr Dowson is now using his expertise in harnessing the power of social media to help far-right activists based in Serbia.
One of those is a medical student called Filip Milinic who runs a nationalist group called Generation Identity, which is part of the flourishing far-right scene in Belgrade.
Mr Milinic's Facebook page says he works for the Serbian Radical Party, whose leader was convicted of war crimes last month.
"We are against the mass immigration, illegal immigration... basically, we do not want to be replaced, to be bred out of existence in our own homelands," he explains. "That's our number one goal."
Mr Milinic says Mr Dowson has given his group social media training, gaining it thousands of Facebook followers.
"Now we have over 7,000 likes on Facebook, it has been very helpful," Mr Milinic adds.
Mr Dowson has denied giving training, but says he has advised hundreds of groups online.
Matthew Collins, from Hope not Hate, says Mr Dowson "seems to see himself as some kind of benevolent individual now who wants to offer the wealth of his experience and knowledge to other people".
Additional research by Tom Bennett.