Throughout history, mankind has searched for meaning in life and how it can be obtained. Achilleus in Homer's epic poem The Iliad inadvertently comes to understand several core values that he did not set out to discover. Achilleus learns how to have compassion on another human being, he learns that his anger can have undesired and negative consequences and he learns that honor is about more than his ego. Many people view Achilleus as nothing but a cold-hearted killer, but there are several incidents in The Iliad that clearly show his humanity, beginning with the taking of Briseis in which Achilleus not only is angered that his prize is taken from him, but we also see glimpses of him missing her specifically; and again we see Achilleus distraught at the loss of his friend Patroklos, so upset is he that he goes to battle again in spite of Agamemnon; and also at the end of the story when Priam comes to Achilleus to ask for the body of Hektor we see Achilleus moved to pity, all of which show that Achilleus has humanity, he cares for people around him, we just do not see his care come to fruition except in time of great need.
Expounding on the meeting between Priam and Achilleus, we see a radically different character than we have seen in most of the book thus far. In both of the other incidents mentioned above, we see Achilleus angered as much as anything else, but in this incident with Priam, where Priam reminds Achilleus of his own father (in both senses of the word) we do not see anger or any other negative emotions from Achilleus. We see real, genuine human compassion for this man who has lost many sons and has recently lost his favorite son. Achilleus weeps for his own father and for Patroklos first and then turns his pity to Priam and commends him for having the courage to see the man who killed so many of his sons. Before this we don't really see true compassion out of Achilleus, he sits by his ship and not only allows many Achaians to die, but asked the gods for it so that he might regain honor. If we only saw that alone and did not read the closing book of The Iliad we might be justified in calling Achilleus an unfeeling monster, but there seems to be a change in Achilleus after the death of Patroklos; maybe having his dearest friend die on the battlefield makes him realize the finality of death. Perhaps Achilleus didn't realize before Patroklos died that the people he was killing in battle had families and friends because he was too caught up in gaining glory for himself and after Patroklos died he gained new understanding. Of course it is possible that we simply don't see that side of him, but it's more likely that Achilleus had never given it a second thought till it occurred in his own life. So then, in the confrontation between him and Priam we see that Achilleus truly feels pity and compassion for at least three people in his life, Patroklos, his father and finally Priam who is reminiscent of Peleus, a kind of pity that we have not seen from Achilleus up to that point.
We also see in Achilleus' life the consequences of his anger that come to fruition that he had never expected. Achilleus is a picture of what happens to people who allow their passions to master them, taken to extremes. He becomes so angry at the loss of Briseis that he actually wishes devastation upon the Achaians, and in his anger he does not think through all of the possibilities of this wish. He counted on the loss of many Achaian lives, as that would make them come to him for help, restoring his honor. But when he allows Patroklos to go out into battle he does not consider the possibility of Patroklos dying, so when it happens it is a shock to him. What Achilleus learns is that our plans and desires can have adverse effects; he never planned on someone he cared about die in battle as a result of his dispute with Agamemnon but nevertheless it happened. This is great commentary on our lives and how we plan things, because we can wish for one thing and not see the negative effects that it might have because we are blinded by the original desire. Much like in William Shakespeare's Hamlet, Prince Hamlet desires revenge on his uncle for murdering his father, but he does not predict that so many people around him would die in the process, including his own mother and Ophelia.
But Achilleus also learns that honor is about more than his own pride and ego being lifted up; it is about a deeper sense of respect. When Achilleus was chasing down Hektor around the city, Hektor begs him to respect his family and allow him a proper burial, but at this point in time he was so consumed with rage that he forgets all about the Greek codes of combat and desecrates Hektor's body for days. He relearns some of this honor, again with the visit from Priam. Priam comes to Achilleus at great risk, and Achilleus chooses to hear him out rather than simply kill him or capture him. If Achilleus had captured the king of Troy, his honor among the Greeks would have been great indeed because it probably would have ended the war quickly. But instead he chooses to hear Priam out and return Hektor's body to him, and he takes it a step further and cleans the body before giving it back so that Priam would not be distressed. It can be argued that Achilleus shows more honor in returning Hektor to Priam than in all the rest of the book, despite his great deeds on the battlefield. This act shows his compassion, shows his respect for Priam and in the end shows that his concern is now for things outside himself.
The story of The Iliad contains many themes and can be used to reveal many truths about human nature, but the story of Achilleus drives the action of the story and acts as a microcosm of the course of many human events. And despite many misconceptions about the character of Achilleus, he is more than killer, he is more than a mindless machine, he is a human being who learns and grows and experiences pain and triumph through the tragedies that he experiences. He is like us in many ways, he acts impulsively and is selfish and thinks of himself, but he changes and he is not the same person that he started the war as. We see a different person over the short period of time over which The Iliad takes place, imagine how different he is from the very beginning of the war.