Leif is a major character in the Jugdral timeline of the Fire Emblem series. He first appears as a supporting playable character in Seisen no Keifu and as the protagonist of Thracia 776.
Seisen no Keifu
Leif is the prince of Leonster and the son of Quan and Ethlyn, making him the cousin of protagonist Seliph. He is also the brother of Altena.
His next appearance is as the protagonist of Thracia 776, a midquel of Seisen no Keifu, taking place between chapters 5 and 8 of the previous game.
Leif appears in the 3DS game Fire Emblem: Awakening as both an NPC in several DLC battles and as a unique downloadable character. The player will unlock him for use after completing the Xenologue battle Lost Bloodlines 1. His concept art is done by Sachiko Wada of Sacred Stones.