A Mercenary found in Celica's route. The rest is a quote from the Fire Emblem Wiki. 

"A coarse seaman with a dry sense of humor, Saber frequently debates at Celica's orders and often calls her out on her idealistic nature, aware of the necessity of violence. Despite this, Saber shows loyalty to whoever employs him and although jaded in his views in contrast to Celica, Saber pledges his loyalty to her after the reveal of her identity, showing his willingness and desire to fight for her cause."

Saber's english voice is David Sylvain. https://youtu.be/6MsB4vZ0YnM?t=580