In Dark Souls, the Soul of Sif is the boss soul used to forge the Greatsword of Artorias.
The Soul of Sif is obtained by defeating Great Grey Wolf Sif in Darkroot Garden. At the Giant Blacksmith in Anor Londo, it can be used with the required weapon and upgrade materials to create versions of the Greatsword of Artorias. The soul can also support other Sif-related equipment choices, so players should check the desired recipe before consuming it.
The weapon’s name refers to Artorias, the legendary knight associated with the Abyss. Its lore and requirements make Sif’s boss soul unusually important, especially for players pursuing achievement completion or collecting unique armaments.
This fact is commonly confused with the Soul of Artorias, which is tied to the Artorias boss encounter in the expansion and is not the standard material for the Greatsword of Artorias. The exact weapon path also matters when choosing the base weapon.