Slaine is a young boy of average height. He wears the uniform of the Mars Orbital Knights. Slaine is shown to be very friendly with Princess Asseylum, being completely loyal to her. When presented with the possibility of her being alive, he boldly went after her alone.

Slaine was born on Earth. His father was a scientist sent to study the ALDNOAH drives. He and his father were rescued by the royal family, having to work under them, he slowly developed a strong bond with the Princess. Because he was born on Earth, he faces a lot of discrimination from the people of Mars.

(Source: ALDNOAH.ZERO Wikia)