Yama no Okina, known in Japanese as 山の翁, is a mysterious Assassin-class Servant in Fate/Grand Order and the title borne by the Grand Assassin, a legendary figure associated with death and judgment. He appears as an imposing, hooded, skull-masked warrior who serves as a powerful enforcer of mortality. In the series, he acts as a near-mythic presence, intervening when the balance of life and death is at stake, and is portrayed as an embodiment of the concept of the “Old Man of the Mountain.”