Lore
He is the brother of Selen Vinland and part of the Vinland Family. He is also the guardian of Maiden Astrea. He wears Dark Silver armor: "Known as the oldest of metals, the dark silver is said to purify dark malice. It protects the user from all magics." He also wields the weapon Bramd: "A dreadfully enormous coarse-iron hammer. One of Vinland's treasures. Its distortion is the mark of an old giant killer, and it increases the wielder's resistance to plague and poison."
The Vinland Family are a renowned and powerful family in the religious groups of Boletaria, with both of their children seen in game being high ranking holy knights. Both Garl's helmet and, in the Remake, the Vinland Family Crest depict a "sacred tree" relevant to their family line, potentially the reason for their place in the church hierarchy. In the original game, the crest depicts a grape bunch, mirroring the family name Vinland, which literally translates to "wine land". The house likely provides from their land for the wider area, or directly to the church. However, even without this fortunate background, Garl Vinland has made a name for himself as a powerful and devout knight, easily wielding the massively heavy Bramd in one hand, even when weighed down by the equally heavy Dark Silver Armor and his Dark Silver Shield.
It is no question, then, as to why he came with Maiden Astraea alone to the Valley of Defilement, as the Lady needed no other guard. As she grew to pity the natives, so did Garl, who mirrored her feelings and supported her even when she chose to become an Archdemon. Though wholly human to the end, he defends her with his life, urging the Player to leave them in peace. His blessed life until this journey is likely why he too cannot see the hypocrisy in Astraea's choice. If he is killed first, Astraea, knowing she cannot fight the Player, will kill herself in sorrow and spite. If she dies first, he will remain alive, but his death is unnecessary to obtaining her Demon Soul. If you leave the area he will leave his weaponry. If you have Pure White World Tendency, he will appear after the fight as a Black Phantom in his usual spot, which is the only way to obtain the Vinland Crest.
Theories
Garl Vinland is Maiden Astraea's Lover
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