The Dagger of Mortis, also known as the Mortis Dagger, was a powerful artifact located on the Altar found within the Wild Space world of Mortis. The Father concealed this weapon on Mortis as a mechanism to exert control over his offspring, namely the Daughter and the Son. This dagger possessed the capability to govern the actions of this pair of potent Force wielders, and, if the situation demanded it, to bring about their death. However, if the dagger was used against the Father, his demise would strip his children of their immortality.
Upon learning of the emergence of the Chosen One, a Jedi of prophecy, within the galaxy, the Father orchestrated the arrival of Anakin Skywalker, a Jedi Knight believed to be the Chosen One, to his realm on Mortis. Despite Skywalker's successful completion of the Father's test, thus confirming him as the Chosen One, he declined to assume the Father's position on Mortis, as the Father was nearing death. Subsequently, the Son attempted to sway Skywalker toward the dark side of the Force, prompting the Daughter and Obi-Wan Kenobi, Skywalker's former Jedi Master, to secure the dagger from the Altar of Mortis in an attempt to restrain the Son.
The Son managed to seize the dagger from the Jedi, resulting in the death of Ahsoka Tano, Skywalker's Padawan. When the Son then tried to murder the Father, the Daughter stepped in, becoming the victim instead. The Son, devastated, abandoned the dagger, and the Daughter's remaining essence was channeled to revive Tano. In a last-ditch effort to subdue the Son, the Father turned the dagger upon himself, thereby divesting the Son of his immortality and enabling Skywalker to inflict a fatal blow with his lightsaber. This action restored balance to the Force on Mortis, and the dagger, along with the entire world, vanished in a brilliant white flash emanating from the Father's monastery.