He is based on the real life emperor Nero.
Pre-Trials of Apollo
Nero was born in in 37 AD, the last of the dynasty of Julius Caesar. He was responsible for the fire of Rome and only acted when the flames threatened his manor. He was married three times and became a widower as many times. He burned Christians alive at his parties. When he was thirty he became a god-emperor.
Nero has influenced many events in history via Triumvirate Holdings, also using the company to supply funding to both Luke Castellan (during Percy Jackson and the Olympians) and Octavian (during The Heroes of Olympus).
At an unknown point in time, Nero killed Meg McCaffrey's father Philip, and proceeded to take in and raise her as his own daughter. Through his sophisticated manipulation over the years, Nero lead her to believe that he and "The Beast" (which he claimed killed Meg's father) were two separate people and made her unquestionably loyal to him.
The Trials of Apollo
The Hidden Oracle
Nero first appeared talking to Python in Delphi. After Meg and Apollo (who was trapped in a mortal form as punishment by Zeus) found the antechamber to the Grove of Dodona, they finally see that he is trying to burn down the grove. While Apollo tries to save the grove and his restrained demigod children Kayla and Austin, Nero orders his Colossus Neronis to attack the camp, while fleeing himself, along with Meg and her Karpoi (grain spirit) servant Peaches.
The Dark Prophecy
Nero is seen in Apollo's dream ordering Meg to capture Apollo. He has a Germanus guard and a man named Marcus go with Meg to make sure nothing happens. However, Meg escapes them and returns to Apollo. He also appears in a flashback with a six year old Meg looking at the dead body of her father on the steps of Grand Central Station. It is also said that he took away Peaches, claiming that Meg did not deserve a "pet" and gave him to his fellow Triumvate Holdings member Commodus, how attempted to kill Peaches, but was stopped by Apollo and Meg.
Kane Chronicles Villains
Magnus Chase Villains