Mother, I need new armour so I can fight to avenge my best friend.
Ah! Achilleus! You're alive?
When the Trojans see Patroklos, they think he must be Achilleus - because of the armour - and become absolutely terrified. Then Hektor kills Patroklos - with the help of the Apollo and a minor Trojan warrior named Euphorbos.
When Achilleus learns of the death of his friend, he swears revenge. He sends his mother, Thetis, to get a new suit of armor made for him by the fire-god, Hephaistos.
The next day, Achilleus rejoins the battle and kills many Trojans, including Hektor in a one-on-one battle.
For the next few days, Achilleus abuses Hektor's body in gruesome ways, even after Patroklos has received a proper funeral. The gods don't like this, and tell him to stop.
When the Hektor's father comes unarmed to ask for his son's body, Achilleus agrees.