Gatrie

Fire Emblem: Path of Radiance
Gatrie originally joins Ike's party in Chapter 5, alongside his friend Shinon. But, at the start of Chapter 8, they leave due to their lack of confidence in their new leader. He returns as an ally in Chapter 13, but can only rejoin the main party permanently if Astrid, who is also recruitable in that chapter, has a conversation with him.

Fire Emblem: Radiant Dawn
Gatrie will automatically be recruited along with the rest of the Greil mercenaries