Semele was a mortal woman who was loved by Zeus. Zeus promised to do anything for her, and she wished to see him in his full form. Knowing that any mortal who saw him in his full glory would perish, Zeus revealed himself and Semele perished instantly. However, Zeus managed to snatch Semele's unborn child, and that child became Dionysus.
Eventually, she was brought back from the dead by Dionysus, where she was brought into Mt. Olympus where she dwelled with the Twelve Olympians.