King Arthur is a legendary British leader who, according to medieval histories and romances, led the defence of Britain against Saxon invaders in the late 5th and early 6th centuries AD. The details of Arthur's story are mainly composed of folklore and literary invention, and his historical existence is debated and disputed by modern historians. The sparse historical background of Arthur is gleaned from various sources, including the Annales Cambriae, the Historia Brittonum, and the writings of Gildas. Arthur's name also occurs in early poetic sources such as Y Gododdin.

Arthur King may refer to:

• Arthur Henry King (1910–2000), British poet, writer and academic
• Arthur Scott King (1876–1957), American physicist and astrophysicist
• Arthur King (footballer) (1887–?), Scottish footballer
• Arthur King (boxer) (1927-2011), Canadian boxer of the 1940s and '50s
• An alias of DC Comics supervillain Merlyn