Jim Atherton, 53, from Washington, Tyne and Wear, flew to the Middle East to reportedly join up with a Christian militia group who are fighting the Islamist extremists.
The father of three and grandfather of two was described by friends as a quiet man who kept himself to himself and had no army experience.
Speaking to The Sun, he said: "I'm prepared to die fighting IS.
"I'm not a young bloke, I had a heart attack in 2007. But it's something I felt I had to do. I wanted my grandkids to know what I'm really about."
Neighbours said he was a brave man, fighting for his country.
Howard Williamson, 68, a former labourer who has lived on the street for 40 years said he knows him very well.
"I think he's doing a hell of a job and it's really good of him," he said.
"He's a much braver man than me, I have known him for a lot of years. He's a tough man to go out there.
"He didn't mention it before, just packed his bags, sold his car and done a flit.
"The family are not very pleased about it, that's what I know. I don't think his wife is very happy.
"I think he's doing a hell of a job going out there, he's fighting for the country and it's a good thing.
"I didn't believe it when I first heard, he's got no experience going in the army.
"He's a nice lad and I get on with him very well, he's quiet and always keeps himself to himself. I hope he gets back in one piece."
Mr Atherton told The Sun he raised £18,000 to pay for his travel and weapons by selling his Sierra Cosworth, two motorbikes and a boat.
He said: "Watching what IS are doing just beats me up. I couldn't stand seeing them killing woman and children willy-nilly.
"People were commenting online about IS atrocities then five minutes later it was all forgotten.
"Nobody seemed to be doing anything about it, so I decided that I would."
The Sun said Mr Atherton had already come under mortar and rocket fire as he protects Christian villages in Iraq.
He said he flew to Turkey and was turned back initially but returned a second time and was able to get a flight to Iraq.
He has since equipped himself with a machine gun, a pistol, a shotgun and a grenade.