* After having a mostly-white first series, Riordan's branching out in ''Kane Chronicles'' and ''Heroes of Olympus'' to include more ethnically diverse casts.
* As of House of Hades, he has blindsided ''everyone'' by adding an LGBT character to the Percy Jackson/Heroes of Olympus canon in the form of [[spoiler: Nico di Angelo, who has his hidden crush on Percy dragged out of him by Cupid in front of Jason]]. IN A CHILDREN'S SERIES. PUBLISHED IN PART BY DISNEY.
** His statement regarding this on his website's FAQ, in particular:
-->''"I am committed to writing appropriate books for the middle grades. This means no bad language, no gratuitous or explicit violence, and no sexual content beyond what you might find in a PG-rated movie expressions of who likes whom, holding hands, and perhaps the occasional kiss. The idea that we should treat sexual orientation itself as an adults-only topic, however, is absurd. Non-heterosexual children exist. To pretend they do not, to fail to recognize that they have needs for support and validation like any child, would be bad teaching, bad writing, and bad citizenship."''
** He takes this further in ''The Hidden Oracle'' by [[spoiler: pairing Nico off with Will Solace]], thereby establishing the first LGBT couple in the franchise. Not only that, but [[spoiler: ''Apollo himself'' is explicitly confirmed as bisexual]]! The best part is that ship in question is portrayed as healthy and completely non-sexualized, even in-universe with the narrator adding his two cents on the concept. It really says something about how far we've come in being able to show things like this in children's media, and ''major'' props to Rick for being completely unabashed about it.
** Even further in ''The Hammer of Thor'' by [[spoiler: having a genderfluid transgender main character, Alex Fierro, and having Magnus all but explicitly confirmed as pansexual because of his crush on Alex as both genders. Non-binary genders are rarely talked about or shown in any media and to have Alex and Magnus discuss being transgender and talk about non-binary genders in a ''popular children's book'' and to have someone in that group as a love interest is absolutely groundbreaking.]]
* Depending on whether you thought it was shoehorned in or not, Magnus' small jab at cultural appropriation could be seen as this, because it is indeed an insensitivity issue that many trivialize.
* The ''Gods of Asgard'' series and ''Trials of Apollo'' both have heavy focus on emotional abuse with guardian figures, with Hearth's father forcing him to pay an impossible debt of tasks, Samirah and Alex being used by Loki, and Meg being controlled by Nero by way of the Beast, a "second personality" that "comes out when she misbehaves". Really heavy and serious stuff, but, again, an important issue to address that few young readers' stories would attempt to include with such a serious and multifaceted approach.