Remarkable researches carried out by writer and artist Yuri Leitch are reinstating at long last the downgraded "god of Glastonbury", Gwyn ap Nudd, to his rightful place in the ancient British pantheon.

For centuries associated with the legends surrounding Glastonbury Tor where, as the mere King of the Fairies, Gwyn has been said to reside, he was even demoted to the demon king of the Celtic Underworld by early Christian missionaries.

But after years of delving deep into the myth, including painstaking study of medieval Welsh literature and legend, Yuri has found that Gwyn was originally the Winter King, a protective warrior god and astrologer with a crucial relationship to the Glastonbury Zodiac.

And Yuri's findings are now forming part of an academic programme in Germany which is studying the Winter King tradition across the whole of northern Europe.

To the ancient Britons, says Yuri, the isle in the marshes that was later named Glastonbury by the Saxons was known as Ynys Wydrin, the Glass Isle; it was their beloved sacred ground, as well as the threshold of Annwn, their otherworld paradise, and Gwyn was its protector, the British Lord of Paradise.

Yuri who, despite his first name, is half Welsh and half Scottish – his parents named him after the Omar Sharif character in the famous film Dr Zhivago, based on Boris Pasternak's novel – arrived in Glastonbury eight years ago.

He had an interest in the town's legends, and became fascinated by the fact that Gwyn's was the only one relevant to the Michael Line – the perceived alignment across southern England of historic sites associated with St Michael, including the Tor, and oriented to the Mayday sunrise. So there must be more to the "rather twee" story of the King of the Fairies than met the eye, Yuri thought. As the centuries passed, Gwyn had come to be depicted as a kind of pantomime character. "But he turns out to be one of the old gods of Britain," said Yuri. "Welsh medieval writings have lots of stories about him. I studied all of them and he became a much more intelligent cultural figure."

Gwyn was hailed as the Winter King who had to do seasonal battle with the Summer King each year on Mayday, Yuri believes. The tussle is also symbolised by the annual phenomenon of the sun rising at midwinter along the outline of the Tor when viewed from Windmill Hill, at the time the year turns back again towards summer.

Y uri also connects Gwyn with the winter constellation of Orion, mirrored in a landscape effigy adjacent to the Glastonbury Zodiac and which appears to be supporting the zodiacal wheel. "The native or pre-Roman Britons were much more intelligent than we give them credit for," said Yuri.

"Because they were pre-Christian we tend to see them as barbarians, but they weren't. They had quite a complicated, cultured and civilised lifestyle and their groups of gods and goddesses were just as complex as those of Rome and Greece, and they had sacred landscapes.

"They were the descendants of the people who built Stonehenge and Avenbury, and Glastonbury seems to have been, to them, a sacred island." There is no known image of Gwyn, but Yuri says he could be represented by a white stag and that placenames around Glastonbury support this theory.

"I have been reluctant to create an icon and say this is what Gwyn looks like," said Yuri. "Probably what I'm going to do to sidestep that is some artwork of a white stag, suggesting it as a symbol of Gwyn."

If you'd like to learn more about this fascinating legend, Yuri is giving a talk at the Mystic and Earth Spirit Fayre at Glastonbury Assembly Rooms on Sunday – St David's Day – based on his illustrated book, Gwyn, published by Temple of Wells, Somerset, at £11.99. Visit Yuri's website at www.yurileitch.co.uk