Athena’s role in Homer’s Iliad actually starts before the text itself. She is one of the three goddesses who wish to be awarded the apple Eris throws to provoke disent among the wedding guests. Partly in anger over the apple being awarded to Aphrodite, she decides to support the Greeks.
Her first intervention in the Iliad occurs in Book I when she prevents Achilles from killing Agamemnon. In Book 2, as she continues to do throughout the Iliad and Odyssey, Athena gives good advice to Odysseus concerning how to manipulate the Achaeans.