"Jupiter" is a proper name, he was an important Roman god. You may know the god Zeus for the Greeks, well Jupiter, that was the equivalent but for the Romans. He is the son of Saturn, husband of his sister Juno. He is the deity of the sky, of lightning and thunder. That was Jupiter, who is roughly the equivalent of Zeus for the Greeks.
This expression has its origins in Greek mythology. Greek mythology is all these stories that were invented at the time of the Greeks. There were lots of myths, invented stories, stories told. These stories have passed down through the generations of Greeks, Romans, up to the present day. There are lots of very, very well-known, very, very famous stories, which often had a moral.
And here in this story it is Dionysus, who was the future god of wine, who was born out of Jupiter's thigh. So Dionysus was born out of Jupiter's thigh in Greek mythology.
Today, of course, when we talk about someone who believes he came from Jupiter's thigh, obviously, we don't think of someone who would be a god, the future god of wine, Dionysus, no. We usa whatsapp number data use it to describe someone who believes he is, who thinks he is someone exceptional, remarkable. There is obviously, here, a notion of someone pretentious, someone we say full of himself, someone who loves himself a lot, who thinks he is the best. If we say that someone believes he came from Jupiter's thigh, we simply mean that he is pretentious, that he loves himself a lot, that he thinks he is the best, that he is exceptional.
You understand, I think, the general
Imagine, you are at work and you are talking with a colleague during a meeting, you are discussing etc. He is a new colleague who has just arrived in the company and who is very pretentious and who criticizes you, who thinks he is the best. And you say: "No, but who does he think he is? He really thinks he is born from Jupiter's thigh". By saying that, you indicate that this person, he thinks he is exceptional, he thinks he is remarkable, he thinks he is someone remarkable, he is pretentious, full of himself, and you say: "This person really thinks he is born from Jupiter's thigh".