“If my bro Valbar's going, then I'm going too. I've got a bit of confidence in my skill with a bow, y'see.”
—Leo's recruitment conversation in Pirate's Fortress
Leo (レオ Leo) is a playable character from Fire Emblem Gaiden. He is part of Valbar's party. After Dahha is defeated, he joins Celica's party. After the war, he joined the knighthood of the newly formed kingdom of Valentia.
If he survived the previous battle, talk to him at the Pirate's Fortress.
Leo is the only Archer unit available in Celica's route. Archers in Gaiden come with many useful perks that make them one of the better classes in the game. If they equip a Weapon, they automatically bump their natural range of 3 up to 5. When they Promote to Bow Knight, their range is always 5. With a weapon equipped, they also do bonus damage to Flying Units. They are at very little risk of being harmed and can easily pick off weakened enemies or bring them down in health so your other units can finish them off without the enemy hitting them back.
That being said, Leo's starting stats are standard, and his growths are very unfortunate. Archers in Gaiden have very little use for HP or Defense because they outrange all other units in the game. That Leo excels at these defensive stats at the cost of poor offensive growth means he loses major potential as a unit. His Speed base and growth is low enough that he will have difficulty Double Attacking anything, and his Promotions will do nothing to fix this. However, the Archer class is useful enough that these poor growths do not prevent him from being a solid unit. Leo should be able to safely stick back and pelt enemies with little risk to himself, so even with his unsatisfactory stats, there is no real downside to using him.
It is worth noting that Atlas is able to promote into an Archer in Celica's route. When comparing the two, Atlas winds up as a superior Archer as he will have roughly the same Skill and Speed as Leo, but he will have significantly higher Strength which makes him the better unit. Atlas promoting to an Archer is the only real route for him to take where he winds up being superior to other characters of the same class. Paison, the Archer from Alm's route, winds up being a superior attack unit to both Atlas and Leo.
As one of the knights of the kingdom, he works towards the restoration of Valentia.
“I have long desired to fall in battle...”
—Leo's Death Quote in Gaiden