God of the sun, music, poetry, and prophecy. Protagonist of the Trials of Apollo series in which Zeus strips him of his godhood and sends him to earth as the awkward mortal teenager Lester Papadopoulos. His arc across five books is a genuine redemption story - he begins as an insufferable narcissist and earns his way back to godhood by learning what it costs to actually care about someone.

A daughter of Demeter with control over plants and seeds, assigned as Apollo's master when he is cast down to earth. Difficult, unpredictable, and deeply traumatised by her upbringing under Nero. Her relationship with Apollo is the emotional core of the Trials of Apollo series.

A son of Poseidon who discovers his divine heritage at age twelve when monsters begin attacking him. Over five books he grows from a confused kid who can breathe underwater into the demigod at the centre of the Great Prophecy. His fatal flaw is excessive personal loyalty - he would risk the world to save the people he loves. Continues as a major character through Heroes of Olympus and appears in later series.

A son of Hades who first appears as a cheerful ten-year-old obsessed with a card game and becomes one of the most powerful and isolated characters in the series. His arc across both the PJO and HoO series is about surviving grief, accepting his sexuality, and finding that belonging is possible even for someone who lives between worlds.