“Heh, these old bones are still good for something. Farewell, my prince. Live, and grow strong…”
—Jagen if he was made the decoy in Prologue IV of Shadow Dragon
The word "Jeigan" is also used as a term for characters which use up too much exp at the start of the game (only if you choose to use them) and so hinders the other characters' growths.
Jagens are usually promoted Paladins that you get in the first chapter, and appear to be amazing units due to having much higher stats than your other units. However, due to being promoted, a Jagen will usually gain very little experience for quite some time into the game, the original Jeigan being an exception. Originally, Jagens always had terrible growth rates and barely any endgame potential. Recent Fire Emblem games are abandoning this trend, however, with the Jagens in Fire Emblem: Rekka no Ken, Fire Emblem: The Sacred Stones, Fire Emblem: Path of Radiance, Fire Emblem: Radiant Dawn and Fire Emblem: Awakening moving toward being Oifeys and all ending up as decent units that are worthy of using.
Oifey - A character and archetype who starts out promoted as well, but unlike Jeigans, their higher stats can enable them to be more useful later in the game.