All that is left of Deddington Castle is a ditch, a mound and a grassy bank topped with trees, but thisparadise for dog walkers was once the headquarters of the second most powerful man in Britain, Bishop Odo.

Depicted on the Bayeux Tapestry on horseback, waving a baton during the Battle of Hastings, he has gone down in history as a cruel killer who helped the Norman invaders to lay waste to Saxon England, amassing a large fortune in land and gold — and then betrayed his half-brother, William the Conqueror by fomenting rebellion.

Chroniclers described him as: ‘ambitious’, ‘rapacious’, ‘greedy’, ‘ruthless’, ‘arrogant’, ‘tyrannical’ and ‘destitute of virtue’ – one called him a ‘ravening wolf’.

Orderic Vitalis, a chronicler monk, creates an unattractive image of Odo as a regent who abused his responsibilities, oppressing the poor and unfairly seizing England's wealth and land.

But now he has a defender, in the form of Trevor Rowley, a lecturer at Oxford University’s Department of Continuing Education.

He said: “You just have to mention Odo and people shake their heads. But he was no worse than most of his contemporaries. He just had a bit more energy.”

The one date in history that everyone remembers, 1066, is entrenched in the English psyche as a symbol of invasion.

“There is this idea of England under the Norman yoke, and certainly, the first 20 years or so after the Norman Conquest would have been pretty awful, but things recovered quite quickly.

“I would not have liked to be an English landowner between 1066 and 1080. It would have taken all your negotiating skills to survive, I think. There was not a great number of executions, but there was a great deal of disruption and laying waste to land.”

Mr Rowley believes Odo’s biggest legacy is the Bayeux Tapestry, which he commissioned to be made, probably at St Augustine’s in Canterbury.

He is said to have contributed 100 ships to the invasion fleet, and the embroiderers showed Odo active in battle.

The tapestry shows William listening to Odo in council beforehand, implying Odo was the architect of the invasion.

Mr Rowley said: “This may be an exaggeration — probably due to the fact that it was Odo himself who commissioned the tapestry — but he was certainly an important figure in the conquest.”

William reorganised his new kingdom and made the loyal Odo the richest tenant-in-chief in the kingdom. A Sunday Times ‘Rich List’, covering the period from 1066 to 2000, put Normans in three of the top four places, with Odo at number four. In his book, Mr Rowley reports this with apparent relish, but adds that it was ‘a dubious honour, dubiously calculated’.

A geographer by training, Mr Rowley spent most of his working life making academic research accessible to a wider public. Now 70, he arrived in Oxford in 1969 to teach archaeology and local studies at the university’s extra-mural studies department, retiring in 2000 as deputy director of what is now the Department of Continuing Education.

During that time, he helped to build up the department’s reputation in landscape history, and still lectures. This term’s course, The Villages of Oxford, will cover the history of Headington, Cowley, Iffley, Marston and Wolvercote.

His new role (“no committee meetings”) has freed him to write more books on the Normans, explaining the modern scholarship that has overturned many received ideas.

“Most of the new work has been published in academic papers and theses, but I realised that no one had written a book about Odo,” he said.

As for Deddington, Mr Rowley believes that it was a major centre, and would have been developed into a stone castle, typical of the later Norman period, had Odo not been imprisoned after raising a private Army on the Isle of Wight, probably in a bid for the Papacy.

Mr Rowley believes Deddington was a military stockade — the centre of Odo’s Midlands empire.

“It was his intention to develop something like Kenilworth as a big military base, but he doesn’t have time to do this because he has fallen by 1082. It would have been interesting when the Bishop of Lincoln built up Banbury Castle — that would have taken the wind out of Deddington. You might have had a similar situation to Kenilworth and Warwick, and the same rivalry.”

As for Odo: “He lived life to the full. He was not just a Norman bully. He built cathedrals, commissioned the Bayeux Tapestry. He could fight, but he was a good administrator. He revolted, he wanted to be Pope (we think). He was an extremely influential man but I don’t think he was any more unpleasant than the others. He was a single-minded money-maker.

“In his 60s, which was old in those days, he went off on a crusade, so he was one of the relatively few people who fought at Hastings and went on the First Crusade.”

If Deddington deserves a bigger role in descriptions of our Norman history, does he think the site should have more prominence?

“I am a big fan of Odo and I think it would be worth having a bigger interpretation centre. The problem is that you have a lot of maybes. But I am prepared to say Odo built this, and that this was his midlands headquarters.”

Mr Rowley is now busy with his next project, a portrait of William the Conqueror for a series called Giants. Then he will get stuck into a book about the landscape of the Bayeux Tapestry.

* Odo, William the Conqueror’s Half-Brother is published by the History Press at £16.99