The Singing Sword is the primary weapon of the fictional character Prince Valiant, a Knight of the Round Table in the service of King Arthur in a long running comic strip of the same name. Prince Valiant was created by Hal Foster in 1937.
The Singing Sword's first appearance in Prince Valiant lore was in the "Ilene Abducted" story first published in 1938. In this story, the original owner of the sword is Prince Arn of Ord, Valiant's rival for the beautiful maid Ilene. The two men put aside their differences when their beloved is kidnapped by Viking raiders on her way to Ord. Arn gives Valiant the charmed sword so that he can hold off their pursuers while Arn rides ahead to free Ilene. The pair continue to work together to rescue Ilene, but their efforts prove futile when they discover she was killed in a shipwreck. Arn permanently gives the Singing Sword to Valiant after this adventure and the two part as friends. Later in the series it is mentioned that the Singing Sword is a sister to King Arthur's Excalibur.
On October 20, 1991, the animated television series The Legend of Prince Valiant offered its own version of the Singing Sword's origins in an episode entitled, appropriately enough, "The Singing Sword." In the episode, Valiant follows his best friends Arn and Rowanne back to Bridgeford and learns that they've been captured by the ruthless Baron Duncan Draconarius. They are sentenced to death as part of the baron's plot to keep Camelot a secret from his subjects. Rowanne's father Cedric loans Valiant the Singing Sword to aid him in overthrowing the baron. According to Cedric, the sword was forged with the same metal that made Excalibur and will be safeguarded by his family until its true owner appears. The sword "sings" during Valiant's duel with Draconarius, indicating that he's a just, pure-hearted man and the sword's destined owner. It sings a second time when Arn wields it while liberating a monastery. Prince Valiant sees this as a sign that Arn is ready for knighthood and uses his sword to dub his friend Sir Arn of Camelot.