Troilus (English: or ; Ancient Greek: Τρωΐλος, romanized: Troïlos; Latin: Troilus) is a legendary character associated with the story of the Trojan War. The first surviving reference to him is in Homer's Iliad, composed in the late 8th century BCE.

In Greek mythology, Troilus is a young Trojan prince, one of the sons of King Priam (or Apollo) and Hecuba. Prophecies link Troilus' fate to that of Troy and so he is ambushed and murdered by Achilles. Sophocles was one of the writers to tell this tale. It was also a popular theme among artists of the time. Ancient writers treated Troilus as the epitome of a dead child mourned by his parents. He was also regarded as a paragon of youthful male beauty.

In Western European medieval and Renaissance versions of the legend, Troilus is the youngest of Priam's five legitimate sons by Hecuba. Despite his youth he is one of the main Trojan war leaders. He dies in battle at Achilles' hands. In a popular addition to the story, originating in the 12th century, Troilus falls in love with Cressida, whose father Calchas has defected to the Greeks. Cressida pledges her love to Troilus but she soon switches her affections to the Greek hero Diomedes when sent to her father in a hostage exchange. Chaucer and Shakespeare are among the authors who wrote works telling the story of Troilus and Cressida. Within the medieval tradition, Troilus was regarded as a paragon of the faithful courtly lover and also of the virtuous pagan knight. Once the custom of courtly love had faded, his fate was regarded less sympathetically.

Little attention was paid to the character during the 18th and 19th centuries. However, Troilus has reappeared in 20th and 21st century retellings of the Trojan War by authors who have chosen elements from both the classical and medieval versions of his story.