Lester Papadopoulos

In The Trials of Apollo, as a mortal, Apollo appears as a Caucasian sixteen-year-old of average build with blue eyes and dark curly hair.

Apollo is described as arrogant, self-centered, and cocky, as is typical among the gods. However, in The Trials of Apollo his personality progressively changes as he starts to feel guilt and sorrow, becoming more empathetic and kind. This is especially shown in Chapter 27 of The Hidden Oracle when he sings about Daphne and Hyacinthus, the most famous of his lovers, taking the responsibility for their deaths. However, he does have a big ego as said in The Tyrant's Tomb when Reyna rejected him.

He has been obsessed with haikus ever since he visited Japan and also appears to obsess over other kinds of poems, depending on where he visits. In The Titan's Curse, Zoë Nightshade briefly mentions that after Apollo visited Ireland, he obsessed over limericks for a time.

He loves his 'little' sister Artemis, even though they often clash, as he is the more laid back, less serious twin; he is always hitting on her Hunters as well, though she has forbidden it, and they refuse to be charmed by him due to their oath. He was also shown to have good relations with his demigod relatives, such as Percy, as demonstrated by how he illegally helped him during one of his quests (though a prominent reason for his help would be because Artemis was in grave danger), and offering to teach him archery.

However, Apollo also has a dark cruel side: he placed a terrible curse on his son, Halcyon Green, for trying to defy fate to help another in need. As shown in Percy Jackson's Greek Gods, one of the factors that fueled Apollo's dark side was his protectiveness of his mother, Leto - after Niobe insulted Leto, Apollo ruthlessly killed all seven of her sons. Later on, he personally asked Hades to eternally torture Tityos for harassing his mother. He even went as far as to flay alive the satyr Marsyas after winning their musical contest, although he later denied having flayed him alive, implying that while he can be quite cruel when angered, he is not so cruel as to painfully kill others.

As revealed in The Hidden Oracle, Apollo's sunny and optimistic demeanor actually conceals deep sorrows: he had never truly moved on from the two greatest loves of his life - Daphne (who turned into a tree to escape his advances) and Hyacinthus (who died due to a feud between Apollo and Zephyros), and was haunted by their memories, to the extent where anything that could be associated with them would almost reduce him to tears if he saw it. Apollo also acknowledged to himself that he secretly harbored a good deal of resentment towards his father, Zeus, and his killing the Cyclopes who forged Zeus's lightning bolt had not been a rash decision, as it was easier for him to hate and blame the weapons which his father frequently used to threaten him with, than to hate his father himself.

Apollo was also revealed to have a tendency to brag about his previous accomplishments, particularly his victory over Python, to the point of embellishing it: though he told storytellers that he had vanquished Python with a single arrow the instant he arrived at its cave, the truth of the matter was that he had needed all of his godly strength, his divine powers, and his bow (which he described to be the deadliest bow in the world) to defeat Python, who had been "no pushover". In fact, the battle between Apollo and Python had been such that the former suffered from nightmares about the latter for centuries.

After being turned into a mortal, it was evident that Apollo could be intensely selfish, given how he viewed his need of regaining his divinity as well as his issues of struggling with his newfound mortality as being more important than the troubles or concerns of others - including those of his own demigod children. However, even in the midst of this, Apollo still proved to be an open-minded and even, in a way, affectionate person, especially to his children: he supported the romantic relationship between his son, Will, and Nico, and when his children made sincere effort to welcome him as one of their own and even promised retaliation on those who dared to target him in his current vulnerable state, he was simultaneously touched by their affection and ashamed of himself for not having done more for them.

Besides this, despite his frequent annoyance with Meg, Apollo grew to truly care for her as a most cherished friend, which eventually led him to acquire the courage and the willingness to admit his own faults and to stand up to Nero. Later on, even after learning that Meg had been a double agent of sorts, Apollo still cared for her and worried about her when she ran away. It's noticed too that despite his fearful behavior, Apollo showed being able to have a great sense of courage, risking his life to save his children, Austin and Kayla, and Meg after they were kidnapped.

In The Burning Maze, Apollo seems to understand more about being a human, and started caring more for the "little losses". When fighting with Caligula, he was willing to sacrifice himself, because he knew this would be the best chance to save his allies. Even though he says he probably wouldn't have done this if Medea wasn't going to heal him and doesn't see it as something heroic because of that, Meg says it was heroic especially for a god. After Jason's death, Apollo even cried on the plane on the way back for everyone who had sacrificed themselves. Apollo still brags about himself and acts like a god, but now he is more sentimental and protective of his friends.

In The Tower of Nero, after regaining his godhood, Apollo struggles to remember how to be a god again and not just a mortal. After awakening, he is horrified by the thought that he may have been asleep for centuries and thus will never see his friends again who all likely think him dead. The experience gives Apollo a new view of his "wicked stepmother" Hera and a sympathetic stance towards Dionysus. He also comes to terms with his relationship with his father and vows to never forget the lessons he learned as a mortal.