It's called Le Morte D'Arthur, so who else would it be about? Even when the story strays from the king to explore the adventures of other knights, it is still mainly concerned with the Arthur; the other knights the story followed are only important because they're his knights. When the Knights of the Round Table are out adventuring, they send all their conquests back to Arthur to pay him homage. When they conquer a region, it becomes Arthur's. He's got the power, the crown, and the Queen. Friends, countrymen, Shmoopers, all roads lead to Camelot.