“Zofia's forces can't compare to the might of the knights of Rigel. If the Kingdom of Rigel makes a move, we won't stand a chance.”
—Fols in Gaiden
Fols (フォルス Forusu, also translated as Force in some of the fan translations) is from Fire Emblem Gaiden. He works directly under Clive in the Zofia Liberation Army. After the war, he joined the knighthood of the newly formed Kingdom of Valentia.
Fols and Clive can be found at the end of the Liberation Headquarters. Defeat the undead monsters within, and talk to them both to have them join your party.
Fols is an average unit. No matter which Soldier/Armor/Baron unit you choose to use in Gaiden, they will wind up very similar. The Armor characters in Gaiden are more heavily impacted by their Promotions and strict class role as a defensive tank than they are by their stats or stat growth, as they will all have high Strength and Defense with low Speed.
Fols is in direct competition with Luka, as they are both Soldiers that you obtain early in Chapter 1 of Alm's route. When picking between the two, Fols comes with some notable advantages. He starts with higher HP, and will likely retain that HP advantage. He will also end up with more Speed and Resistance than the other Armors, and he ends up with much higher Strength than Luka or Valbar. Although Fols has bad Defense growth, all Armor units in Gaiden have similarly low Defense growth and enough base Defense to make Physical attacks do negligible damage anyways. His main notable weakness is his very low Skill, giving him the worst Accuracy among all Armor units.
As one of the knights of the kingdom, he works towards the restoration of Valentia.
—Fols' death quote in Gaiden.