Semele was a mortal princess and mother of the god Dionysus.
Percy Jackson's Greek Gods[]

Dionysus, her son.
Zeus noticed Semele one day and the two entered a relationship. When Hera found out she went to her and made her doubt Zeus was who he said he was and to have him swear on Styx to give her anything she wanted. The next time they met Semele, who was pregnant, had Zeus swear an oath on Styx to show her his Divine Form, he tried to talk her out of it to no success but she was insistent. He reluctantly did so and was killed. However Zeus managed to save their unborn child and sew him into his thigh until he was old enough. Later, Dionysus saves Semele from the Underworld, and makes her immortal.