Arthur was born to his mother Iqraine, and father, King Uther. Throughout his childhood Arthur's mother was married to another man. He grew up with a step father instead of his biological one. It was kept a secret from Arthur that he was a king.
With time Arthur became a king because he pulls put a sword from a stone. He eventually as a king succeeds due to his abilities of defeating enemies. AS time went on Arthur decided to expand his abilities by helping others along with his knights.
Surround the castle!
Sir Lancelot, one of the knights, falls in love with Queen Guinevere, Arthur's wife. He tried to resist his feeling for the Queen as much as he could but such action was impossible. This leads to the downfall of Arthur's kingdom as he discovers the affair.
I have died!
Arthur decides to punish his wife by burning her at the skate. Sir Lancelot saves the Queen from her punishment. At the battle to save the Queen Sir Lancelot accidentally kills Sir Gareth and Gaheris. This causes Arthur to go to war with Lancelot.
Arthur departs from England wit his forces and surrounds Sir Lancelot castle in France. He leaves his kingdom in hands of Sir Mordred to take care off. While King Arthur was gone rumors were being spread that he died in battle.
Sir Mordred faked Arthur's death so he can take power over the kingdom, such decision leads Arthur no option but to return to England. In the battle to fight Sir Mordred, King Arthur and Sir Mrodred wounded each other, and the king died.