McGregor is a background character in Fire Emblem: The Sacred Stones. He was a high-ranking priest of Grado and a tutor in history for Prince Lyon, as well as for Prince Ephraim and Princess Eirika of Renais, during their time in Grado, and apparently lectured Ephraim a lot for not taking his duties seriously.
When Lyon intended to use Grado's Sacred Stone for research, Father McGregor strongly opposed and denied him direct access to the stone. However, after the death of Emperor Vigarde, Lyon finally gained access to it and the shaman Knoll reveals that Lyon executed him personally for opposing him. Before his death, he was able to inform the cleric Natasha of the secret so she could warn the other nations of Vigarde's transformation.