The main characters of the poem are Endymion, a shepherd, and Cynthia, his beloved. Endymion is involved in the action during the entire four books, but Cynthia is often not present or appears in her alter ego form, the Indian Maiden. Endymion, as well as the reader, does not know at the end that they are the same person. Learning that information is the key to the fulfillment of his amorous and spiritual quest. The poem is John Keats’s version of a classical story, in which Cynthia is the goddess Diana.

While tending his flocks on Mount Latmos, Endymion experiences a vision of divine, perfect love. Not content with a life of herding sheep, he embraces the mission of finding this ideal woman. The young man is a dreamer, fond of moonlight, who embodies the spiritual rather than earthly matter—and, by extension, also embodies creativity. Resisting his inclination to feel melancholy, Endymion must undergo heroic trials, including sojourns underground and under the water.

Cynthia, the woman he loves, is an ideal rather than an actual woman. Although she has a tangible, highly sensual manifestation, her embodiment is fleeting. She is identified with hunting, the moon, and essential female nature. She appears as the Indian Maiden, a lovely and virtuous young woman whom Endymion initially rejects because of his spiritual attachment to Cynthia.

Glaucus is a mortal who lives beneath the sea, where he had been condemned to spend a millennium. He had erred by loving the maiden Scylla, who inhabits the water’s edge. Glaucus is responsible for pulling the bodies of drowned lovers out of the water. After Endymion arrives and fulfills a prophecy that a youth would help him, Glaucus is restored to life, youth, and love.

Peona is Endymion’s beloved sister. Confused by his visions and dissatisfaction with normal life, she constantly tries to bring her brother to his sense. She appears periodically to give him practical advice, believing that earthly concerns should satisfy him.