The first instance when a god came down to help for her own personal motives is when Hera sends down Athena to stop Achilles from killing Agamemnon in fit of rage.
"And as this tumult swayed him, as he slid the big blade slowly from the sheath, Athena came to him from the sky. The white-armed goddess, Hera, sent her, being fond of both men gripped his red-gold hair." (Book I; 157-64)
Hera despises the Trojans and rather than watch Achilles kill Agamemnon she decides to intervene and calm Achilles down by offering him an abundance of gifts. " break off this combat Here is my promise, and it will be kept: winnings three times as rich, in due season you shall have in requital for his arrogance." (Book I; 177-82) This scene also contrasts the difference in beliefs between Achilles and Agamemnon. Achilles respects the gods and knows that it is in his best interest to sheathe his sword and not allow his hubris to cloud his judgment. Yet Agamemnon will not allow anyone, human or divine, be better than him or tell him what to do and takes Briseis from Achilles. Shortly after this, the Achaeans go to Troy to call a duel between Paris and Menelaus to end the war. Venus watching this knows she has a vested interest in the Trojans, but more specifically Paris and Helen. The two begin to duel and just as it appears Menelaus has defeated Paris and awaits the final blow Venus steps in.
" choked by the chin strap, cutting into his throat-a well-stitched band secured beneath his helmet. To his own glory, Menelaos now would in fact have pulled him all the way, had Aphrodite with her clear eye not perceived him-and she snapped that band of oxhide, cut from a clubbed ox." (Book 3; 338-44)
In the great love story of this epic, Venus sees the impending death of Paris and knows that if Menelaus kills Paris, Helen will be given to the Achaeans and killed thus ending the love story and the war without the fall of Troy. Therefore her saving Paris from certain death not only allows them to continue their affair but also helps set up the fall of Troy. As the epic continues and the battles become more intense it is clear which gods are on whose side. In an attempt to help the Achaeans, Hera devises a plan to make Zeus fall asleep rendering him helpless. She then goes to Sleep and offers him a golden seat and the hand of the youngest Grace. He happily obliges and as soon as Hera beds Zeus he is put in a deep slumber and Hera continues to help the Achaeans for her own personal means.
Another interesting relationship throughout The Iliad is that of the gods among themselves. They are worshipped by the humans and thought to be some omnipotent supreme beings that hold the powers of the universe at their fingertips, however they quarrel just as humans do. It is this quarrelling and bickering that leads to the next motive to help the humans, gods favors to other gods. Just as humans befriend others and hold allies, so to do the gods. It is this relationship between the gods that, unfortunately for the humans, can change the tide of war at any given time simply for calling in a favor. After the argument between Achilles and Agamemnon, Achilles cries out to his mother...