Jupiter

Jupiter (Iuppiter in Latin) is the Roman counterpart of Zeus. As Jupiter, he becomes more 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.

History
Jupiter is the supreme god of the Roman pantheon, called dies pater, "shining father". He is a god of light and sky, and protector of the state and its laws. The Romans worshipped him especially as Jupiter Optimus Maximus (all-good, all-powerful). This name refers not only to his rulership 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 oracles. His English name is Jove.

He had a temple on the Capitol, together 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 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.

The Lost Hero
When Jason is found by Annabeth 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 the attention of not Zeus, but Jupiter. He is mentioned several times during The Lost Hero and The Son Of Neptune.

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 was Jove (Iovi in Latin).
 * Jupiter is referred to as Optimus Maximus, meaning "best and greatest" in Latin.