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The Scarlet King is one of the overarching antagonists of the SCP Foundation series. He is an ancient and evil god who is portrayed as a ruthless powerful monarch often tied to the destruction of the current world as we know it.

He serves as the unseen antagonist behind the articles SCP231 and possibly SCP2317, and the main antagonist of the "Verse of an Endless Song" series. He is one of the many anomalies proposed for the title of "SCP001", an entry originally written for the 2018 Doomsday Contest.
Appearance

In the tale "Three Short Scenes About Death" the Scarlet King is given a little description. His fist are described as massive and gnarled, holding the chains of his consorts and concubines. The same fists could effortlessly smash a man's throat. The King's voice is described as similar to "the chittering of a billion infinitesimal insects", and swirling and constantly moving. His voice also was neither "high nor low nor cacophonous nor methodical", simply just being. When the Scarlet King first appeared to the Serpent, he took the form of a girl in red clothes sitting on a rocking throne.

According to Tufto's SCP001 Proposal, the King is more akin to a living idea than an individual entity; in effect, he is the idea of nihilism and a force of chaos, and can assimilate an entity thought to be him into an aspect of himself just as it did with SCP2317K. He is always depicted as figure with a crownlike ornament over his head showing royalty and associated with the color red, or in the cases of alien cultures lacking the perception of the color red the King would be associated with a color that would be synonymous or close with the color. In SCP4989, Dr. Simon Kells described looking at the King "like staring at a Pattern Screamer only more hollow". When a group of Foundation agents confronted the physical form of the Scarlet King in his supposed throne room, he appeared as a young malnourished boy with hanging messy hair, crimson red eyes, wearing only a tunic and beaten sandals, and covered in blood, having taken the form of the first child who was sacrificed in his name.

In "Dr. Wondertainment Goes Out With A Bang", the Scarlet King was described as having an anorexically thin humanoid body, standing exactly seven feet tall and emitting blinding red light. His skin resembled that of a burnt corpse, his hands were gnarled claws, and possessed two great antlers behind his head and multiple eyes on his face. When confronting Cornelius Wondertainment he wore a military uniform covered in medals and rank markers.

In SCP5641, the Scarlet King was described as ten trillion times Skanda's size, possessing seven mouths which spoke profanities, eyes that killed anyone who looked into them, and fourteen hands which he used to form all types of mudras. In SCP6765, the King's body was described as a humanoid with a bleeding red maw surrounded by grasping arms and eyes while clouded by smoke and fire, and poured endless blood and released an endless inhumane scream.

In ROUNDERHOUSE's Jade Proposal, the Scarlet King was depicted as a gigantic androgynous red humanoid being with an obscured face and always accompanying his avatar who was depicted as a sleeping man with a long beard, an elaborate headdress and carrying long spears across his back. When approached by Greaves the Scarlet King took the form of a vast red sea, and when he took possession of the lieutenant, manifested at first as Greaves' nervous system glowing red before taking the appearance of a 3 meter tall skinless humanoid with a bare skull, large horns resting atop his head and inscribed with pulsating symbols and markings.
The Scarlet King was shown to be a cruel, manipulative, and nihilistic individual. After learning about the true cruel nature of existence, he thought that reality should not exist and became hellbent on destroying everything, especially the tree of knowledge, by any means necessary, enslaving and devouring numerous gods and doing whatever pleased him. It is believed that if SCP999 were to interact with the Scarlet King, then his heart would change and finally see the beauty of the world and abandon his quest of destruction.