Eurydice in Wikipedia

Eurydice (Εὐρυδίκη, Eurydíkē) (yur-ID-ih-see) in Greek mythology, was an oak nymph or one of the daughters of Apollo (the god of light). She was the wife of Orpheus, who loved her dearly; on their wedding day, he played joyful songs as his bride danced through the meadow. One day, a satyr saw and pursued Eurydice, who stepped on a venomous snake, dying instantly. Distraught, Orpheus played and sang so mournfully that all the nymphs and gods wept and told him to travel to the Underworld and retrieve her, which he gladly did. After his music softened the hearts of Hades and Persephone, his singing so sweet that even the Erinyes wept, he was allowed to take her back to the world of the living. In another version, Orpheus played his lyre to put Cerberus, the guardian of Hades, to sleep, after which Eurydice was allowed to return with Orpheus to the world of the living. Either way, the condition was attached that he must walk in front of her and not look back until both had reached the upper world. However, just as they reached the portals of Hades and daylight, he could not help but turn around to gaze on her face, and Eurydice vanished again from his sight, this time forever...