King Arthur

I know that King Arthur is a person who live a long time ago. He is real person in the world.
But I didn't know who King Arthur was.
Arthur became the king of England. He always had a prognosticator next to him.
The prognosticator adviced him how to make nice country.
One day, Arthur fall in love with one lady. Then the prognosticator didn't allow to marry her.
Because it was not good future for Arthur. One day the prognosticator came back haven. Arthur marryed her.
Finally, he died. Is dieing him cause her??? In this book, there arehardly particular all of then.
In the first place, I cannot think that there was the prognosticator in rial world.
Second, if he died cause her in the prognosticator, I want to know more deep it.
Do you know about King Arthur??? Is it rial??????