The Great Dog Demon was a powerful yokai lord who ruled the Western Lands and was known throughout Japan. Never formally addressed with a name, he fathered two sons by two different mothers: Sesshomaru from his consort, an unnamed dog demoness, and InuYasha from a human woman (unnamed in the manga, but named "Izayoi" in the third movie). The Great Dog Demon is first mentioned in chapter 12 of the manga as InuYasha's father, "a demon dog that prowled the lands of the west".
The Great Dog Demon's major foe in the manga was the dragon Ryuukotsusei, whom he could not kill but sealed onto a cliff face with his claw; Myouga calls this battle the "cause" of his death.
The gateway to his tomb is hidden in a black pearl (a mystical gem that creates a path between the mortal and spirit worlds) inside InuYasha's right eye. Within the pearl, their father's body is shown as an enormous dog skeleton in a suit of armor: his true form, according to Myouga. The sword Tetsusaiga, forged from the Great Dog Demon's own fang, rests inside this cavernous skeleton, protected by a barrier that repels any non-human with malice toward humans. Because of this, InuYasha inherits the sword rather than Sesshomaru.
Inuyasha and Sesshomaru are known for their strained relationship, despite being brothers. One of their many disagreements and battles is for their father's sword, Tessaiga. Although Inuyasha inherited it, Sesshomaru continues to fight for it and attempts to take it from Inuyasha.