This might get me some hate mail, but I've never really been a fan of the Harry Potter series (the books or the movies). I don't dislike them; I've just never really been able to get into them as much as everyone else on the planet seems to be. Call me crazy, but I guess I'm just not into wizards. (I know, I know... what's wrong with wizards, since I'm clearly obsessed with vampires, witches and almost every other supernatural magical being.) Lil' Lilith on the other hand, did read the books and watch the films (except the last two, which no one has taken her to see yet - I'm not gonna). She also has read almost all of the Percy Jackson & The Olympians series - and we've both seen the film Percy Jackson and the Olympians: The Lightning Thief.
Since I'm not a crazy Harry Potter fan, I would never have noticed the similarities between the two series... however, as Lil' Lilith pointed out to me, there are quite a few.
First off, there's the two male leads - Harry and Percy. Both began their lives thinking that they were simple, mortal, human beings... but then were surprised with the fact that they were special. The former is a wizard, the latter is a demi-god (the son of one god and one mortal). They also kind of look alike - dark hair, light skin, green eyes. Both have very powerful parents that are not in their lives - Harry's father was a pure-blood wizard, Percy's father is the god Poseidon. Both Harry and Percy have a goofy male sidekick (Ron and Grover, respectively) and a powerful female friend (Hermoine and Annabeth).
Both series have a "school" for these special teens to learn more about who they are and how to harness their powers (Hogwarts and Camp Half-Blood) where the students are split into "teams" or houses/cabins, are lead by a powerful leader (Dumbledore and Chiron) and have an intimidating teacher (Professor Snape and Dionysus). Both Harry and Percy have an evil, powerful villain after them (Voldemort and Kronos), have the ability to communicate with animals (Harry with snakes, Percy with horses) and both have an important animal in their lives (owl, horse). Both series also feature a three-headed-dog! The "lightning" symbol is also significant in both series (in Harry Potter, as his birthmark; in Percy Jackson, the lightning thief).
The similarities aren't uncanny. They are probably just coincidental (and if we tried, we could probably find just as many coincidences in other popular series as well) however the Percy Jackson series has actually been accused of stealing from J.K. Rowling's series, which I think is untrue. The concept of an ordinary kid with a troubled homelife who suddenly discovers that he or she is anything but ordinary certainly isn't new. In fact, it's been formulaic way before Rowling picked up a pen.
But let's actually look at the dates - did Rick Riordin, the author of the Camp Half-Blood books, steal from Rowling?
J.K. Rowling finished her manuscript for the first Harry Potter book in 1995. Harry Potter and the Sorcerer's Stone was published in 1997 in London and released in the U.S. in 1998. Rick Riordan finished writing the manuscript for the first Percy Jackson book - The Lightning Thief - in 1994. It was accepted by Bantam Books in 1997 and later sold to Miramax Books before being released in 2005. Neither Rowling nor Riordan could've stolen ideas from each other, because it seems they were coming up with these ideas simultaneously.
It may feel as though the Percy Jackson series has borrowed ideas from the Harry Potter series, because Harry Potter was published first, but Riordan couldn't have copied Rowling's idea. It seems more likely that the publishing company released Riordan's book in order to compete with Harry Potter's endless popularity. There aren't enough good books out there for kids and tweens that actually engage the reader and make them think, so I think there's room for both series on our bookshelf.
[Percy Jackson and The Lightning Thief was directed by Chris Columbus, who directed the first two Harry Potter films.]