Sersi is a member of the Eternals, a species diverted from humanity by experiments conducted by the Celestials one million years ago. She is at least 5,000 years old and became legendary around 1,300 B.C., when the Greek hero Odysseus and his crew, fresh from the Trojan War, came to her island Aeaea. Sersi transformed Odysseus' crewmen into pigs for attempting to menace her. Odysseus, however, managed to ward her off with the aid of the goddess Athena, and Sersi turned his men back to normal. Odysseus spent a year on Aeaea; she also encountered Odysseus' son Telemachus when he came following his father's path. Centuries later, Sersi still considered Telemachus to be the love of her life.
Over the centuries Sersi often interacted with humans, visiting Rome during the reign of Nero, helping Merlin expose an impostor (Merlin Demonspawn) in Camelot, visiting France during the French Revolution, and befriending the English poet Thomas Chatterton.
In recent years, the Celestials returned to Earth to judge humanity, the Eternals, and their other creation, the Deviants. Sersi became involved in the struggle, enjoying the adventure, but caring little for combat. By this time, Sersi had become a famous entertainer in New York, hosting parties at her loft for film stars, super heroes and other influential people. She often entertained with her powers, which her normal human guests believed to be stage magic. Sersi's super-hero friendships eventually led her to join the Avengers in search of adventure and romance, first pursuing Captain America and later the Black Knight. Sersi was a sublime yet powerful teammate until she was driven insane by Proctor, an alternate-reality Black Knight whose Earth had been destroyed by his world's Sersi. Sersi eventually slew Proctor and left the Avengers, operating in the extra-dimensional Ultraverse for a time before returning home and regaining her sanity. She continues to live in New York, occasionally aiding the Avengers and her people against their foes, but preferring her life as a socialite.