|Box title = Seth Diodoros |image = Image:10434.jpeg |imagewidth = 250 |caption = No Image Avaliable |Row 1 title = Age |Row 1 info = 19 (half-blood)
21 (The Return)
22 (The Power, The Struggle) |Row 2 title = Eye Color |Row 2 info = Amber/Gold |Row 3 title = Hair Color |Row 3 info = Blonde |Row 4 title = Species |Row 4 info = Apollyon (formerly)
God |Row 5 title = Occupancy |Row 5 info = Apollyon, Sentinel |Row 6 title = Gender |Row 6 info = Male |Row 7 title = Status |Row 7 info = Alive |Row 8 title = Relationships|Row 8 info = Alexandria 'Alex' Andros (formerly)
Josephine 'Josie' Bethel}pregnant with his child}
“So? What are you going to do about it? Throw your mashed potatoes at me? I'm consumed by terror,"- Seth, Half-Blood
Not much is revealed about Seth's life prior to the book. Like Alex, he had his life monitored by Apollo until a certain point. But in his book called "The Return", he discovered that his last name is Diodoros.
In Apollyon, while connected with Seth, Alex learns that his mother's name was Callista. He says that she was very beautiful, "tall and blond, regal like a goddess," but also "cold and unnapproachable," and always would give Seth hateful stares. In the same book, he also states that he was born, ironically, on the island of Andros.
We also know that before coming to protect Lucian in the first book, Seth had an account of twenty-five daimon kills.
Appearing in the Titan Novels, he starts a relationship with Josie, daughter of Apollo.
Seth is cocky, funny, and very entertaining, but he's also annoying and big-mouthed. It's also noted that he's a player and had never been in a serious relationship before. This might indicate a problem with letting people in due to his upbringing with an unloving mother.
Seth is described as having blonde hair that is pulled back in a ponytail, has a gold complexion, and perfect facial features. He is also described as tall, around Aiden St. Delphi's height, putting him at about 6'5'. Seth is the first Apollyon in his generation and is nineteen years old (said in Pure).
Alexandria Andros: Seth and Alex have a complicated relationship through out the entire series. At first, Seth was bitter towards Alex seeing as she was the reason he was pulled out of the field, but they soon work it out and get along. When Alex is discovered to be the second apollyon, Seth starts to become more possesive of her because everyone believes that she is fated to be with him. What Alex didn't know was that for Seth to become a god killer, he would have to drain her of her powers and energy, most likely killing her.
In Pure, Alex has a lot of nightmares and doesn't sleep well, which also affects Seth because of their connection. Seth starts coming to her room, entertaining her the whole night and sleeping along side with her, as the connetion between them soothed the nightmares away. After Caleb's death, Seth became protective and caring of her, stopping Marcus and Lucian from screaming at her stating that it would only make her feel worse and acting as a guard for her. Whe she was locked up in her room grieving, he didn't allow anyone to come close to her, Guards, Lucian, not even Marcus or Aiden.
When they travelled to the New York Covenant for Alex's inquirement, they would spent hour together training. After the annual Fall Ball, Seth and Alex go for a midnight swim. They both almost kiss, Seth realizes Alex was thinking of Aiden and gives her a choice; to try something that will never work out, refering to Aiden, or try and see what might happen between them, no labels, no promises and no titles. They both kiss three times in this book and have a hot make out session while Alex was on the Brew. In the end, she chooses to be with Seth.
Through out Deity, Aiden and Alex try to figure out a way for her to keep her powers, but it is almost impossible because the power transfer takes place when ever they touch. Aiden realizes that the only way to save Alex is to keep her away from Seth, so he gathers together a small group of trusted people and leaves. At the end of Deity, on Alex's 18th birthday, she becomes a full fledged apollyon and has a strong connection with him, causing her to believe that his beliefs are hers, even when it is the opposite of what she actually believes in. In Apollyon and Elixir, Aiden try's to find a way to break the connection between the two apollyons, but Apollo tells him that the only way for that to happen is for Alex to do it herself. In the middle of Apollyon and end of Elixir, Alex breaks the connection and goes back to being herself.
Aiden St. Delphi: Seth and Aiden have a rivalry through out the series for Alex's affection, but Seth has always had the upper hand since it is believed that Alex and him were destined to be together and becuase Aiden was a pure blood, making a relationship between Alex and Aiden forbiddden.
"Alex, you're starting to worry me. Insult me... or something."