One of the most memorable and defining pieces of the Percy Jackson universe is the question of godly parentage. Demigod children, also called halfbloods in the book series and TV show, are all the children of one of the Greek Olympian gods and a mortal human. Each demigod's parent defines a lot of their characteristics, and they are sorted into various cabins at Camp Halfblood that correspond with their godly parent.

However, there are a few of those cabins that normally stand empty, as there are a few gods who don't have demigod children...or at least, they're not supposed to have any. The gods Zeus, Hades, and Poseidon all struck an agreement to not have any kids, but it's clear in the series that they didn't exactly stick to their words. The big question, particularly for those watching the Percy Jackson show who have not read the original book series, is: why did the Big Three gods come to this agreement in the first place?

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What Are Forbidden Children?

In the Percy Jackson book series by Rick Riordan, the children of Zeus, Poseidon, and Hades are simply called the children of the Big Three. These gods are the "Big Three" because they are three of the most powerful Olympian gods and rule over various domains. Zeus watches over the skies, Hades is the ruler of the underworld, and Poseidon essentially has everything in between, particularly the seas. The children of these three brothers are known as Forbidden Children in the Percy Jackson Disney Plus series, which is a self-explanatory way of describing the fact that they're not supposed to exist in the first place, as the Big Three gods all promised to not have any more children with mortals.

Why Did The Big Three Gods Promise To Not Have Children?

Zeus, Poseidon, and Hades vowed to not have children partially because of the great power, or the potential for great power, that their children possess. In the 1940s, the Oracle of Delphi prophesied that the next child of the Big Three would either save or destroy Olympus when they turned 18. In order to prevent this from happening, the Big Three made their infamous pact that they wouldn't have any more children with mortals, in order to avoid the prophecy and keep Olympus safe. The prophecy is as follows:

There is also another reason for the pact that is brought up in the book series. In the Percy Jackson series, it is occasionally explained that certain historical figures were actually demigods, and that major world events were influenced by the gods. The series states that World War II was actually a conflict between the children of the Big Three, with the children of Zeus and Poseidon being the Allied Powers and the children of Hades being the Axis Powers. Part of the reason for the Pact might also have been to avoid another large-scale conflict between the children of the Big Three.

Is Percy Jackson A Forbidden Child?

Clearly, the Big Three gods didn't quite keep their promises about not having any children, as various children of the Big Three appear throughout the Percy Jackson series, including Percy Jackson himself. Percy is the son of Poseidon, and at the time, he was thought to be the only Forbidden Child that was still alive. Zeus had also broken the pact years earlier when he sired Thalia Grace (as well as Jason Grace, though he doesn't come up until the Heroes of Olympus spin-off series), but she was turned into a pine tree to save her from being killed by monsters from the Underworld that were sent by Hades when he learned of her existence.

Zeus had also previously tried to kill some children of Hades - Bianca and Nico di Angelo - in the 1940s, but was unsuccessful after Hades had them put in the Lotus Hotel (where one remains essentially frozen in time) for 70 years to keep them safe. They factor into the plot later on in the Percy Jackson series, but their story illustrates how much danger the children of the Big Three are in, as their very existence means that the other gods are out to get them in order to protect Olympus. Percy becomes the main threat to the gods in terms of the prophecy, and they all believe that he is the child of the Big Three who will influence the realms of the gods by the time he turns 16.

Percy Jackson & the Olympians

Adventure

Fantasy

Seasons

1

Production Company

Disney

Streaming Service(s)

Netflix

Showrunner

Jonathan E. Steinberg , Rick Riordan

Based On

Percy Jackson and The Olympians

MORE: 5 Greek Heroes That Hades 2 Should Put in the Spotlight