Friar Tuck has been viewed for centuries as a roly-poly, comic addition to Robin of Sherwood's band of merry men. But in the latest BBC series of Robin Hood, which begins tonight, he has been reinvented as a black martial arts expert, to the fury of historians.

David Harewood, the new Friar Tuck, who starred in the BBC thriller Criminal Justice, admitted that this reincarnation of the character had seemed ridiculous to him at first. “I actually laughed,” he said.

Historians are less amused about the casting of Friar Tuck, who is usually played by short, fat, balding white men. There had been rumours that Matt Lucas, the star of Little Britain, would get the role.

Helen Phillips, Professor of English at Cardiff University and an expert in medieval literature, said: “Sub-Saharan Africans wouldn't have been converted by that point, they would have had other religions. North Africans would have mostly been Muslims.

“Also, friars came from upper-class families, as did monks. The kind of families from which friars were drawn wouldn't have been in any sense African.”

Harewood, who was the first black actor to play Othello at the National Theatre, said that he had been persuaded of the merits of the radical interpretation of the character.

“They sent me the character breakdown and it was very different from what I expected. It was a welcome change and something I really felt was going to be exciting,” he said. “Funnily enough, when I first saw Robin Hood when it started three years ago, I thought they'd missed a trick and that they should have had a black character in it. It turns out that I am the black character, so I think it adds a modern dimension to it, as well. I think viewers will really take to it: at least I hope they will.”

In the first episode of the new series, at 6.50pm on BBC One, Tuck has abandoned his mission to the Holy Land and returns to England with the hope of resurrecting the legend of Robin Hood. However, he finds the country a different place. Harewood said: “He wants England to be a place of hope but he comes back to find that the people are slightly broken, much like they are now with the credit crunch.

“The people need a hero, and that's what Tuck very much wants: to stand behind a symbol of good.”

But viewers will at first be led to believe that the friar is a tricksy, brooding character with more on his mind than simply helping the battle against the Sheriff of Nottingham.

“If he did have an ulterior motive, I think it would be to make the country a republic,” Harewood said. “He's not necessarily in love with the country at all. He's very much for the people, by the people, and, if it was up to him, he'd get rid of the monarchy and make it a republic. He wants the people to govern and the people to be happy.

“Tuck is very much his own person. Many times he will go against Robin, argue with Robin and talk Robin into doing things he doesn't want to do. I think he's going to be a challenge to the whole group.”

The actor underwent gruelling fighting lessons for the role, in line with historic interpretations of Friar Tuck as being proficient with “clubbes and staves”. He said: “My stunt double was a kind of a capoeira [a Brazilian combination of martial arts and dance] champion, and there's quite a lot of martial arts that my character does later on in the series, which was really, really fun to do and very physical.”

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