Amphitryon begins with a prologue given by the god Mercury, in which he gives some background information to the audience. Amphitryon and his slave Sosia have been away at war and are returning to Thebes. Meanwhile, the god Jupiter is sleeping with Amphitryonâs wife Alcmena. Jupiter is in the guise of Amphitryon so that Alcmena is unaware that he is not her husband.
Mercury's job is to buy his father Jupiter some time by deceiving those who would interfere. He changes his appearance to look like the slave Sosia, and when the real Sosia arrives, he beats him up and sends him away from the house. Thoroughly confused by having been beat up by himself, Sosia returns to the ship to relay what happened to his master Amphitryon.
The following morning, Amphitryon sets off for the house, annoyed by his slave's foolish sounding story. Jupiter leaves only moments before Amphitryon arrives, and when Alcmena sees her real husband, she is confused as to why he has returned. Amphitryon doesn't appreciate this strange welcome after being gone for so many months, and confusion turns to anger and jealousy after learning that she has slept with a man who is not himself.
After a long argument, Alcmena is ready to leave her untrusting husband but is stopped by Jupiter. He soon begins to set things right, and in a miraculous event, Alcmena gives birth to twin boys. One is the son of Amphitryon, the other is Hercules, the son of Jupiter. To quell Amphitryonâs anger, he explains to him what he did, and Amphyitryon is then honored to have shared his wife with a god.

Question: Who was sleeping with Amphitryon wife while he was away?
Answer: god Jupiter 
Alternative answer: Jupiter