Eren's father
1.
He knows many secrets of Titan, but the only thing he can do is keeping quiet. He has to hide his missing for Eren who has became a soldier fighting titans, meanwhile control his impulsion to revenge for his wife who had been eaten by a titan, otherwise he will die for releasing the top class secret information. He regrets for his invention that can transfer a person to a titan temperately.
Several years ago, a man came to find him for his intelligence in medical discipline. At that time, he was based on limited resources to study the difference between man and titan. He was young and ambitious; he was dreaming that maybe he can do something to help people know more about titan, and then beat them in the future. He was selected to an Institution. This institution has no name. He was guesting that the builder of the institution was King, but he was also wondering why several significant researches did not be published to the public. They were the hopes to lead people to a new life. One of the significant researches is the transformation from human being to special titan. However, it is only a hypothesis, because no one wanted to take the risk of experiment. If the special titan lost his mind, no body can control him. Their researches came to a dead end.