Paul Scott, 63, was described as “cold, callous and calculating” by a judge who heard one of the men involved even told him to “stop it”.
During a trial at Luton Crown Court, a jury heard how Scott’s offences were to “fulfil his own sick fantasies” and may have taken place over three years.
The crimes came to light when the boy, who cannot be named for legal reasons, made a complaint earlier this year.
He told investigators that he had been given something to make him sleepy before the abuse took place.
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Scott, from Ware, had pleaded not guilty to seven charges involving the rape of a child under 13, but was found guilty on six counts.
He pleaded guilty to possessing indecent images of children and breaching a Sexual Harm Prevention Order.
Defending him, Marion Smullen told the court on Friday: “The defendant maintains very strongly that he is not guilty.
“Obviously he is going to prison for a very lengthy time and it will not be a soft option for him.”
But as he was jailed for 21 years, Judge Stuart Bridge told Scott: “You were cold, callous and calculating. Some of the men involved finally told you it had to stop and called you a monster.
“They were absolutely right.”
Speaking after sentencing, Detective sergeant Colin Nelson said: “This abhorrent individual inflicted unimaginable horror on an innocent child.
“He facilitated the rape of a young child on multiple occasions just to fulfil his own sick fantasies.
“He showed no remorse for this horrific and vile sex abuse, denying it completely and forcing the victim to undergo the further emotional trauma of a trial.”
Scott had been jailed in 2011 to three years and nine months in prison for making, possessing and distributing images of child abuse.
A spokesman for Bedfordshire Police said no-one else had been arrested in relation to this case.