Jupiter

Jupiter is the Roman counterpart of Zeus. As Jupiter, he becomes more strict, disciplined, militaristic, and warlike. The Greeks envisioned Zeus as a powerful and proud being, while the Romans envisioned Jupiter as a more formal and stoic version of his Greek counterpart, as well as more responsible.

History
Jupiter is the supreme god of the Roman pantheon, called dies pater, which means "shining father." He is a god of light and sky, and protector of the state and its laws. The Romans worshiped him especially as Jupiter Optimus Maximus (the best and the greatest). This name refers not only to his rule over the Universe, but also to his function as the god of the state who distributes laws, controls the realm, and makes his will known through various Oracles. His English name is Jove.

He had a temple on the capitol, along with Juno and Minerva, but he was the most prominent of this Capitoline triad. His temple was not only the most important sanctuary in Rome; it was also the center of Roman political life. Here official offerings were made, treaties were signed and wars were declared, and the triumphant generals of the Roman army came here to give their thanks.

Representation
The distinguishing character of his person is majesty, and every thing about him carries dignity and authority with it; his look is meant to strike, sometimes with terror, and sometimes with gratitude, but always with respect. The Capitoline Jupiter, or the Jupiter Optimus Maximus, was the great guardian of the Romans, and was represented, in his chief temple, on the Capitoline hill, as sitting on a curule chair, with the lightning in his right hand, and a scepter in his left.

The poets describe him as standing amidst his rapid horses, or his horses that make the thunder; for as the ancients had a strange idea of the brazen vault of heaven, they seem to have attributed the noise in a thunder storm to the rattling of Jupiter's chariot and horses on that great arch of brass all over their heads, as they supposed that he himself flung the flames out of his hand, which dart at the same time out of the clouds, beneath this arch.

The Lost Hero
When Jason Grace is found by Annabeth Chase at the Grand Canyon, he calls the gods by their Roman names instead of the Greek ones. Later that day, Chiron who knows a small bit about his past says that Jason was already claimed. To prove this, Jason calls down a bolt of lightning to prove he is a son of Zeus, but in actuality he is a son of Jupiter.

Later when meeting with Thalia, she talks about how Zeus returned to their mother once after she was born. She described him as being different from how she remembered him, being more forbearing, mature, and fatherly. This is because Ms. Grace had gained not the attention of Zeus, but Jupiter.

The Son of Neptune
While not seen, the Roman demigods have the highest respect for Jupiter. The camp itself is named after him, as well as the largest temple on Temple Hill. The temple is called the Temple of Jupiter and has a large statue of Jupiter holding a lightning bolt inside. When Percy saw it, he commented that his bolt didn't look like that. Later, after the Roman War Games, Mars appeared and told the Romans that while Jupiter doesn't like the gods talking directly to mortals, he gave Mars permission to speak for only a few minutes.

Iris also mentioned Jupiter to Frank, telling him that he was the one that sent the harpies to keep food and drink away from Phineas as punishment for revealing the intentions of the gods to mortals. Jupiter is later mentioned by Juno during her conversation with Percy, admitting to him that she was working behind Jupiter's back in order to bring the two sets of demigods together. She also admits that Jupiter has as a long history of his pride leading him to be wrong on important issues only to be forced to change his stand at a later date.

The Mark of Athena
Jason is said to be a son of Jupiter multiple times throughout the book.

Trivia

 * Jupiter is the namesake of Camp Jupiter.
 * The fifth and biggest planet of the Solar System was named after the god.
 * An alternate name for Jupiter is Jove (Iovi in Latin).
 * Jupiter is referred to as Optimus Maximus, meaning "best and greatest" in Latin.
 * Jupiter, a town in Florida, is named after this Roman god.
 * Frank Zhang states that as Jupiter, Zeus became a more responsible god. This could relate to Thalia describing him as being more fatherly than his Greek aspect, Zeus.