Klein

Klein was born to Lord Pent and Louise, born shortly after the events of The Blazing Blade. He was conceived sometime prior to the fight against the Fire Dragon as Louise reveals her pregnancy during the final battle to Pent. He would later become an older brother with the birth of his younger sister, Clarine.

Klein later becomes the leader of a mercenary group from Etruria. He hired Thea and her squad of pegasus knights. His troop is stationed in the Western Isles when Roy's army arrives there. Klein receives orders to enter a battle against Roy to protect the villagers. However, he is persuaded to switch sides by either Roy or Clarine, and then convinces Thea to do the same.

(Source: Fire Emblem Wiki)