In Dark Souls, Big Hat Logan sells sorceries in Firelink Shrine after being rescued from Sen’s Fortress.
Logan is a renowned sorcerer from Vinheim and is initially found imprisoned in Sen’s Fortress. After the player frees him, he moves to Firelink Shrine and offers advanced sorceries, provided the player meets the relevant intelligence requirements.
His quest continues in The Duke’s Archives, where he studies Seath the Scaleless’s research. After certain events, Logan becomes hostile and can be fought in a transformed state. His story connects the game’s sorcery tradition with Seath’s experiments and the pursuit of forbidden knowledge.
Griggs of Vinheim also sells sorceries at Firelink Shrine, but he is a separate character with a smaller selection. Quelana and Dusk are also spell teachers, yet neither is Logan.