The reigning monarch of the Kingdom of Lucis, Regis raised his son, Prince Noctis, on his own. For long years, he has sustained the Wall, a magical barrier that encases the Crown City, protecting it from invasion. However, tragedy would befall him at the treaty signing with Niflheim, during which he was reportedly slain.
SPOILER WARNING: Details about the Final Fantasy XV story follow.
The 113th king of Lucis met an untimely end in an unanticipated attack on the Citadel. Though he put up a fierce resistance against his aggressors, supporting the the Wall around Insomnia sapped him of his strength and his debilitated state contributed to his demise.