Zeus (Roman Jupiter), son of Cronos, ruler of gods and men, the cloud-gatherer and lord of the lightning flash is the supreme power on Olympus. Often he is easygoing and humours his wife Hera and daughter Athena when they try to cross him - but when push comes to shove he is stronger and far more violent than they could ever be. Even gods can be damaged by a well-aimed thunderbolt!
He likes sex - and is easily won over by a bit of flirtatiousness whether from Thetis (Book1) or his wife Hera (Book 14). For most of the Iliad, he seems to be on the Trojan side because of his promise to Thetis in Book 1 - but he has promised Agamemnon that he will sack Troy (even if Agamemnon himself does not always appear to trust Zeus in this!). The reason - as explained by Menelaus in Book 13: Paris broke the sacred law of xenia when he abused the hospitality of another man. The most fundamental role Zeus had, as Zeus Xenios, was to protect this relationship between host and guest, the only guarantee of civilised behaviour between men in an age before law.
He is subject to fate - he has the power to save his son Sarpedon, but is persuaded not to by Hera. Gods should not tamper with mortals' fate.
Life on Olympus is banal and trivial compared to the momentous happenings on the battlefield: a quarrel between men over honour has huge and tragic consequences - a quarrel between Zeus and Hera merely threatens to spoil the gods' dinner (Book 1).