The Question and Answer section for Iliad is a great resource to ask questions, find answers, and discuss the novel.
Achilles agrees to join the battle after Hector has killed Patroclus.
That would have been Patroclus.
Thetis implores Hephaestus’s to make Achilles a a "killer" set of armour. Hephaestus afrees and forges a breastplate, a helmet, and an ornate shield with the images of constellations, parstoral nature, dancing children, and cities full of men.