The Percy Jackson and Olympians series is the original Percy Jackson series. It has five books:

It is about Percy Jackson finding out the Greek Myths are true and his absent father is really Poesiden the God of the Sea and he is a half-blood. Then Percy Jackson and his friends go on quests & adventures working to defeat Kronos the father of the Gods, who is looking for revenge after getting sent to the bottom of Tartarus by the God's.
Percy Jackson is licensed under CC BY-NC-SA 4.0