When did Rick Riordan first write his book?

Rick Riordan's first published book was "Big Red", a children's novel about a rescue dog, which was published in 1997.

However, he had written other books before that, including a few non-fiction books about history and mythology, which were self-published.

It's important to note that his most famous series, Percy Jackson & the Olympians, wasn't published until 2005.