Despite being a child of Demeter, Dimitri's face and personality lacks diversity in emotions. He doesn't show a lot of emotion in his everyday life. Due to his father teaching him his emotions affect his abilities, he represses his feelings. His morning runs act as a way to get any leftover feelings out. The other campers often question how he can be so friendly yet lack any feelings. It isn't that he doesn't experience emotions, he just doesn't let them control him. He rules by logical and makes choices based on the probability it will succeed or fail, not how it makes him feel.

A man who experiences chaos often craves peace that man is Dimitri. Dimitri despises drama and any kind of conflict. It causes him to choose sides and either way he'll be hurting another person. Conflict also affects his powers since they are controlled by his emotions. Dimitri acts like the peacemaker of the camp since there is plenty of turmoil bubbling. He likes to know the campers feel happy and safe in this new environment and that they have no fears of what may come. While Dimitri tries to remain peaceful and neutral, if peace at the camp is threatened, Dimitri will do anything to make things peaceful again. He's not afraid to use force if it means keeping the peace. He doesn't like using force, but isn't afraid to use it if necessary.

Dimitri isn't all sunshine and happiness, which you wouldn't expect of a child of the goddess of the harvest. He's seen and experienced the negatives of the human world and has been a cause too. His view of the world remains mostly negative, though he's seen the positive sides of humanity. He goes into any situation considering all the bad sides of the situation and how he can fix it. He voices his opinion when he know the bad sides are being ignored, but will stay out of it otherwise. Bad things happen when he's involved so he prefers to keep away.

Regardless of his negative thoughts and emotionless attitude, Dimitri still remains friendly. He enjoys being surrounded by other people and talking to the other campers. Companionship is still something he longs for so he enjoys finding it in others. He takes his role as one of the older campers very seriously, wanting to be a guide to the younger ones. He remembers being scared and alone if an unfamiliar place and doesn't want any of the new campers to feel the same. His kind and friendly moments tend to confuse the campers since he can also be unemotional and pessimistic. Dimitri wants to make the best of his time at camp and tries to do the same for everyone else.

Unlike most of the other demigods, Dimitri was always aware of his parentage and what he was. Worship of the Greek gods began to die out, but the Costas family always believed. The farming family prayed the most to their beloved goddess of the harvest. Demeter found favor in this family, blessing them with a bountiful harvest. The youngest of the Costas family, Alexius Costas treated Demeter with the most reverence. He would visit her temple every day, bringing her offerings and multiple prayers. Demeter loved the human, choosing him to be the father of child. Thus, Dimitri was born, named in honor of his mother.

Demeter was one of the more devoted parents to her children. She made seasonal visits when it was time to harvest the crops, wanting to check in on her 'seedling.' She would only spend a day, but it was felt like a month in Dimitri's eyes. When she wasn't around, his father raised him. As Alexius worked to maintain the family's farm and raise Dimitri, he did little to hide his son's nature from him. He told young Dimitri stories of his mother and past Greek myths. While Alexius regarded his son as a gift, he knew misfortune would follow his son's life; it was only natural for children of the gods. The family's farm was far enough away from the major cities so it was easy to hide when Dimitri's powers flared up, but it was close enough that Dimitri didn't feel so isolated from the outside world. Dimitri's power revealed themselves when he was young. Seeing that his son's powers reflected his emotions, Alexius tried his best to teach his son how to control, or hide, his emotions so his powers would be easier to control. He had to resort to telling Dimitri he was dangerous and was capable of hurting many people. All of this before he was ten.

The Costas family fell into financial hardship on Dimitri's tenth birthday. Looking for ways to pay their debt, Alexius began to borrow money from loan sharks. One particular shark was not happy Alexius hadn't been keeping up with his payments. Unaware of the child in the household, an argument between Alexius and the shark turned violent. Hiding in a closet, Dimitri made himself known when he heard a gunshot, finding his father on the ground clutching his chest. Filled with anger and fear the gunman began to choke, not finding air. Dimitri let him die, hurry to his father. Find his father dead, sadness and anger began to take over. Without his knowledge, a powerful tornado began to roar outside, destroying everything around. Dimitri didn't realize until it was too late what he had done. His family home and the land was destroyed except Dimitri and his father. Digging his father a grave on the family land, Dimitri held a funeral for the two of them before boarding a ferry to the mainland. He didn't want to stay in a place with such painful memories.

Now an orphan, Dimitri spent most of his life out in the forest. He didn't need to worry about food with his abilities and any other necessities he needed he learned to make it from natural resources or would work odd jobs to earn money. He never tried to reach out to his mother. Dimitri feared her reaction about the life he took and destruction he caused. While he regretted destroying his homeland, he didn't regret killing his father's murderer. It was necessary in his mind. He was glad he did it. Dimitri spent his free time getting better control on his powers, not wanting to cause any more disasters. He discovered new abilities and mastered his control of air and plants.

At fifteen, life became lonely for the wanderer. He knew allowing another person into his life could end negatively, but he longed for companionship. He found said companion in a girl he found in the forest. The girl, around his age, was hanging a noose from a tree branch. She was startled seeing another person in the woods behind her house. Dimitri questioned her about the noose and his heart broke at her story. The girl, Callie, was being abused by her parents, tiring of the abuse she decided to end her life. Dimitri wanted to help the girl and offered to take her away. She agreed, but worried her parents would come after them. Dimitri promised to take care of that too. The two made a plan for Callie to pack a bag and they would disappear together. She snuck Dimitri in her house and they would sneak out of her window. Her parents caught them, but before they could harm either of them, they began to choke. Callie closed her eyes, but Dimitri only stared, letting the two adults asphyxiate. A part of him knew he didn't have to kill them, but they deserved to die. After the two died, Dimitri looked to Callie, promising he wouldn't let anyone hurt her. Surprisingly, Callie trusted him and the two left.

The young couple settled in Thessaloniki, Greece. With Callie's skills in the kitchen and Dimitri's power to manipulate plants, she found work as a cook and Dimitri sold produce. The two rented a small cottage, slightly away from the city to still have some privacy. The couple lived happily, never worrying about anything other than normal things like bills and what to eat. Dimitri still hoped his mother gave up on him or assumed him dead. Alas, neither was true. On his twenty first birthday, Demeter appeared to her son while him and his girlfriend while they were sleeping. Sneaking off to speak to her privately, Dimitri desperately begged to be left in peace with his girlfriend. In response, Demeter began to dissuade her son from this idea. She reminded him of how humans would feel if they found out what he was like and that they would try to hurt him, or Callie. Dimitri shook at the fear of causing harm to someone he cared for. Not wanting any harm to come to the woman he loved, he agreed as long as his mother promised to protect and watch over Callie. She agreed. Leaving a note, Dimitri left for Camp Athens. Currently, he acts as a big brother to the younger campers. He's aware of the history of this camp yet he does not fear. All he wants is his mother to keep her promise.