Unlike performers behind character creations Ali G and Alan Partridge, the comic behind Marenghi refuses to speak out of character.
The conceit behind the Perrier Award winning show - Netherhead - is that Marenghi "The One Man Fear Factory" is on an author's tour, introduced by a publicist.
Netherhead is the title of the author's latest, darkest work which features an amateur Egyptologist's descent into the netherworld.
Last year Fright Knight - a show introducting the Marenghi character - was nominated for the Perrier Award.
The fictitious writer, whose previous works include Rupture, The Dank and Eye Sore puts the inspiration for the new work down to illness earlier this year.
Risible horror
"I'm not sure, because I did have flu at the time, but I believe I might have sold my soul to the Lord of Darkness for this tale," he said.
Mood music, bad masks and risible horror tales complete the scene as the show is a parody of paperback horror novels and their writers.
The performers behind the show refuse to reveal their names or backgrounds to the press.
But there are rumours that he is the creation of Matthew Holness supported by an on-stage publicist played by Richard Ayoade and Alice Lowe as his ice-queen girlfriend.
They are thought to be former members of the Cambridge Footlights team.
Since they will not throw off their guise, we must return to the world of Garth Marenghi.
Marenghi is an alarmingly prolific novelist - publishing his debut Sliver, a book about a flying knife, at the age of 25.
He has not looked back since bringing such novels as Ooze ("Can water die?"), Crab! and Black Fang ("Big scary rats learn to drive").
Marenghi's publicist was on-stage at the Perrier Awards to laud the writer's inclusion in the mainstream.
"We are delighted that the genre is finally getting the recognition it deserves.
"Garth has had a lot of flak over the years from people who have said: 'Why is he writing another book about crabs that kill babies?'"
The Fringe success has led to slots on Radio 4 for the author and a place in the London-bound Best of the Fringe show.