Byleth "Professor, Emblem of the Academy" Eisner

About

Byleth is a playable character and the main protagonist in Fire Emblem: Three Houses. As an Avatar, their name, gender, and birthday are customizable. Byleth serves as a professor at Garreg Mach Monastery. They possess the mysterious Crest of Flames and can wield the Sword of the Creator.

Byleth appears in Fire Emblem Engage solely in his male form as an Emblem. Emblem Byleth's spirit is housed in the Ring of the Instructor. When the Emblem Rings were distributed across Elyos, the Ring of the Instructor was one of the six rings retained in Lythos. Shortly after the awakening of Alear from their thousand year slumber, Lythos was attacked by Elusia who raided the Ring vault, stealing the four Rings there, including the Ring of the Instructor. Princess Hortensia would use Byleth's ring during her fights against Alear and their forces until she eventually joined them. Upon recovering the ring, Alear purified it of Sombron's corruption, allowing them and their forces to utilize his power.

(Source: Fire Emblem Wiki)