To this day, King Arthur’s actual historicity remains disputed. However, according to literary lore, his greatest deed was the Battle of Badon, which was a resounding victory for the Britons and which stopped Anglo Saxon invasions and expansion for a while.
The legacy on the other had is quite real: it is a founding myth of the kingdom of Britain and also a fundamental part of European medieval culture. Geoffrey of Monmouth in the 12th century wrote a semi fiction book about King Arthur and Camelot. However, it was Chretien de Troyes’ literary, artistic work on Arthur that was the basis for the legend as we know it today. Other famous literary works are Thomas Malory’s Le Morte d’Arthur and Alfred Tennyson’s Idylls of the King.