Prince Valiant in the Days of King Arthur, often simply called Prince Valiant, is an American comic strip created by Hal Foster in 1937. It is an epic adventure that has told a continuous story during its entire history, and the full stretch of that story now totals more than 4600 Sunday strips. The strip appears weekly in more than 300 American newspapers, according to its distributor, King Features Syndicate.

Edward, the Duke of Windsor called Prince Valiant the "greatest contribution to English literature in the past hundred years". Generally regarded by comics historians as one of the most impressive visual creations ever syndicated, the strip is noted for its realistically rendered panoramas and the intelligent, sometimes humorous, narrative. The format does not employ word balloons. Instead, the story is narrated in captions positioned at the bottom or sides of panels. Events depicted are taken from various periods from the late Roman Empire to the High Middle Ages, with a few brief scenes from modern times (commenting on the "manuscript").

While drawing the Tarzan comic strip, Foster wanted to do his own original newspaper feature, and he began work on a strip he called Derek, Son of Thane, later changing the title to Prince Arn. King Features manager Joseph Connolly eventually renamed it Prince Valiant. In 1936, after extensive research, Foster pitched his concept to William Randolph Hearst, who had long wanted to distribute a strip by Foster. Hearst was so impressed that he gave Foster ownership of the strip. a magical blade apparently created by the same enchanter who forged Arthur's Excalibur. Val helps his father regain his lost throne of Thule, which has been usurped by the tyrant Sligon, and later travels to Africa and America.

When the strip starts in 1937, Val is five years old. The first episodes follow the youth through the wild Fens district of Britain with his father, the deposed King Aguar of Thule. When Val encounters the witch Horrit, she predicts he will have a life of adventure, but he will never be happy or content. Arriving home, Val discovers that his mother has died. Not long after this come encounters with Gawain, with gigantic creatures and with the glory of Camelot. Steve Donoghue comments: