He first started out as the heir to the Bern throne and son of King Desmond and Queen Hellene. His father watns him out. He and Guinevere love each other but Desmond wants that to end. Jaffar a Black Fang assassin almost kills the young heir but Nino stops him.
Zephiel, now king of Bern, is the main villain of Fire Emblem: Fūin no Tsurugi. In this title, Zephiel's sanity is slipping away from him, and he seeks to rid the land of Elibe of humanity by allying himself with dragons.
Many years after the events of Fire Emblem: Rekka no Ken, Desmond attempted a second assassination by handing his son a goblet of poisoned wine. Zephiel fell ill from the poison, but did not die. However, with the help of his close ally Murdock, he stayed in hiding and had a false funeral arranged. When Desmond stepped up to the casket to view Zephiel's body at the funeral, Zephiel, now in his lust for revenge, rose and stabbed his father to death.
A few days later, Zephiel used the Fire Emblem to awaken Demon Dragon Idenn. Shortly afterwards, the dragon Jahn sends an illusion of himself to confront Zephiel about his motives, and when it is revealed that they have similar goals, the two started working together. After this, Zephiel ordered his army to take over the continent of Elibe. The nomad and myrmidon kingdom of Sacae was attacked by a force led by Brunya and the first to fall. Next was the mercenary and pegasus knight kingdom of Ilia, with the Bern forces led by Murdock. Then he personally led the attack on the Lycia Alliance and gravely wounded the marquess of Ostia, Hector. Then he forged an alliance with the Kingdom of Etruria, and caused a rebellion there. He personally went to an attack himself with Flaer, Nacien, and Percival, and knocked out Cecilia. When he left, and the Lycian army was noticed, Nacien left Flaer to command, and he was killed by Roy. Later, in chapter 23, Zephiel sends Brunya with Idenn to the Dragon Temple to complete his plan and later faces Roy, who slays him.
Zephiel appears in Nintendo vs. Capcom as an unlockable playable character. He has a projectile move that goes across the floor called the devil shot. In Story Mode involves how he built his empire ending with a bloody battle with the Takeda clan. In his ending he releases the Takeda men Shingen, Yukimura and Sasuke who were begging for their lives as he doesn't need strength or wisdom form the Takeda.