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
Bibliography: Fitzgerald, Robert. The Iliad. New York: Alfred A. Knopf