Arthur, also known as Chester King, is the founder of the Kingsmen and the hidden quartenary antagonist of the 2015 movie Kingsman: The Secret Service after revealing himself as an affiliate of Richmond Valentine.
In the Movie
The Dog Shooting Training and New Lancelot
Eggsy, along with several other candidates, are recruited to become Kingsman agents, but during a test in which Eggsy has to shoot his dog JB in order to pass, he fails and Roxy becomes the next Lancelot.
He also watches live on a video feed as Harry fights in a corrupt church and Harry is killed by Valentine after killing all the members of the church.
Betrayal and Death
Later, as Arthur and Eggsy toast to the deceased Harry, Eggsy finds out that Arthur had become one of Valentine's converts and Eggsy manages to trick Arthur into drinking the poisoned brandy.