Some gods in Greek mythology were the products of a god's affair with a human. Though these gods were not Olympians they still shared in the glory of the gods. Two of the most renowned half-mortal gods were Dionysus and Heracles.
Zeus was know to disguise himself as a mortal to win the affections of a beautiful woman. One such affair was with the daughter of King Cadmus of Thebes, Semele. Zeus had laid with Semele and she was with child. Six months later Hera found out about Zeus' affair and decided to interfere. She disguised herself as one of the family's neighbors and went to counsel Semele. She asked how the maiden could be sure that this lover was not a monster. She then told Semele that if this mysterious lover truly loved her he would reveal himself to her in his true form.
Semele followed her advice and made the request of Zeus. When she told him that he could no longer come to her bed unless he granted her wish Zeus became angry. He then appeared to her as lightning and thunder and she was killed instantly. Luckily Hermes saw this and saved the unborn child. Hermes then sewed the child up in Zeus' thigh so that the child could finish developing. Three months later the child emerged from the thigh of Zeus fully grown. Because of this strange double birth, Dionysus is often referred to as the "Twice-born" or "The child of the double door."
Another one of Zeus' mortal affairs was with Alcmene, granddaughter of Perseus and Andromeda. Perseus' kingdom had been at war with the Taphians. Electryon, son of Perseus, lost all eight of his sons in the war. Electryon then left his kingdom to avenge his sons and left his nephew Amphitryon in charge. He had promised Amphitryon that if he ruled well he could marry his daughter Alcmene when he returned. While Electryon was away Amphitryon paid a large ransom for some stolen cattle. Upon Electryon's return Amphitryon demanded the ransom repaid. When Electryon refused, Amphitryon through a club and it rebounded and killed Electryon.
Amphitryon then fled to Thebes with Alcmene and planned to wed her. Alcmene refused to marry him until he finished avenging her brother's deaths as her father had planned to do. Amphitryon agreed and went on his journey. Zeus seeing his chance disguised himself as Amphitryon and claimed to have finished with Alcmene's request. They then laid together for three nights and days. The next day Amphitryon returned home and began to tell Alcmene about his conquest. Alcmene then said that she was tired from not sleeping the night before and that he should not expect her to listen to his story two nights in a row. Amphitryon, confused by Alcmene's statement, went to an oracle and discovered what had happened. Fearing Zeus would become jealous, he never bedded his wife.
Nine months later Zeus was boasting about how his new son, Heracles (Glory of Hera) was going to be born that day. He was so confident about the birth that he declared that any prince born before nightfall to the House of Perseus would be King. Hearing this Hera went to the mother's doorstep, tied her clothes in knots and knotted her fingers to slow the birth of Heracles. That night Eurystheus was born and since Zeus could not go back on his word he became king. One hour after nightfall Heracles was born and the next night Heracles' twin, Iphicles, was born.