Since 'altruism' means 'feelings and behavior that show a desire to help other people and a lack of selfishness', and this word 'altruistic' ends with -ic, we can assume, based on its structure, that this is an adjective that is used to describe a person who behaves in such a way.
Assuming that you're talking about the myth of Greek Gods, the purpose of the myth is for an Explanation of natural Phenomena. For example if sailors in that era were trapped in a massive storm in the middle of the sea, they will say something like : "we've angered the Poseidon"
