Arthur was hidden for his father's safety and his own safety from the Unseelie Court. His father, Uther was supposed to give him to the court as a part of the deal they made.
Merlin a wizard , took Arthur to a village to never be found by the Unseelie Court. He was taken as a child and never really knew his parents, Uther and Igraine. He was raised by this "father" Sir Ector.
Sir Ector knew about Arthur, and when Ulric came to their village Ector told Arthur to make sure he does not tell anyone his true identity. Ector told him to be his brother Cie's squire if anyone were to ask who he was.
After Arthur pulled Caliburn, Ulric and he fought each other for the throne and the kingdom of Albion. Arthur defeated Ulric for the throne and now rules Albion and renamed the kingdom Camelot.
King Arthur helped the people of the kingdom feel safe by unifying the warring tribes around under one rule and having food to spare for the first time in years.