Medusa

spoiler hiddenMedusa is a Greek mythological figure described as a winged human female with living venomous snakes in place of hair. Those who gazed upon her face would turn to stone.
spoiler hidden
spoiler hiddenWith her older sisters spoiler hiddenSthenospoiler hidden and spoiler hiddenEuryalespoiler hidden, they made up the three Gorgon Sisters who inhabited the Shapeless Isle. She came into existence thanks to the thoughts and prayers of humans, who desired a perfect goddess, but she was cursed for her beauty and turned into a monster hated by all. She is thus not a Heroic Spirit but a monster closer to a Divine Spirit.

spoiler hiddenDue to her nature, she can manifest through different aspects depending on which disposition is predominant (more or less monstrous)

In Fate/stay night:
spoiler hiddenShe is the Rider-class Servant of spoiler hiddenShinji Matouspoiler hidden in the Fifth Holy Grail War of Fate/stay night.

In Fate/stay night: Heaven's Feel:
spoiler hiddenShe only truly acts as spoiler hiddenSakuraspoiler hidden's Servant when their connection is revealed in Heaven's Feel.

In Fate/Grand Order - First Order:
spoiler hiddenShe is a Lancer-class Servant. Medusa is Blackened, a process by which a being is tainted by an outside force, causing their personality to be reversed toward the orientation of evil.

In Fate/Grand Order: Absolute Demonic Front Babylonia:
spoiler hiddenIn this singularity Medusa manifests as two separate beings:

spoiler hiddenOne is Ana, a Lancer-class Servant without a Master. This incarnation represents the young Medusa, from a time when she wasn't known as the monster inhabiting the Shapless Ile. Though still wary of humans for casting her away, she is much closer to the perfect Goddess she was supposed to be.

spoiler hiddenThe other one is Gorgon, an Avenger-class Servant. This incarnation represents Medusa as a man-eating monster. The burning hatred against the humans that exiled her and her sisters led her to become the very monster they accused her to be. Gorgon wields Tiamat's Authority which grants her the ability to generate Demonic Beasts.