Orochi

"Monster King" Orochi ("怪人王"オロチ, Kaijin-ō Orochi) seems to be the leader and strongest member of the Monster Association. He is one of the main antagonists of the Monster Raid and Super Fight arcs.

Appearance
Orochi is a large and ominous-looking monster. He has several large spikes pointing upwards above his head, cracked skin, empty eyes, and a multiple set of pointy teeth inside his mouth. His shoulders, wrists and fingers have the appearance of monstrous snakes' heads with pointy teeth, with the latter ending in large claws. His knees have the appearance of snake skulls and his clothing consists of a large cape connected to a circular, veiny joint in the center of his chest and a piece of cloth covering his lap.

Personality
Orochi has a serious demeanor. While a monster, Orochi doesn't outright kill humans immediately if they catch his interest like Gouketsu. This is shown when, instead of finishing the martial artist off after defeating him, he captured the first Super Fight Champion and offered him greater power as a monster after torturing him.

He also has little tolerance for failure from his subordinates since he eats Awakened Cockroach after he failed to kill Genos.

History
Several years ago, Orochi battled and defeated Gouketsu. Instead of killing the martial artist, Orochi took him to the Monster Association Headquarters and gave him an offer to help the martial artist gain more power in exchange for cooperation.

Super Fight Arc
Gyoro Gyoro is speaking with Orochi about the monster raid's situation.

After Tatsumaki killed the Hundred-Eyes Octopus, Gyoro Gyoro finds the situation troublesome, but Orochi sees it as not a concern because they can make as many Mysterious Beings as they please.

Through his robot Bofoi questions Orochi and Gyoro Gyoro about their goals and while they tell him destruction is a natural part of a monster's instincts, it is not their end goal.

He killed and ate Awakened Cockroach for his failure to kill Genos. He was about to do the same on Do-S, but spared on behalf of Gyoro Gyoro's request. He realized Gouketsu isn't present in the meeting and sent Gyoro Gyoro to find him, but was too late, as Gouketsu was unknowingly killed by an unknown hero who will happened to be go on par with Orochi's power level.

Abilities and Powers
Due to his large stature and his epithet as the "Monster King", it could be assumed that he is one of the strongest monsters in the Monster Association. Gyoro Gyoro also stated that Orochi is above all of the Monster Association's main forces. While unseen, Orochi apparently was strong enough to defeat the martial artist Gouketsu, the first Super Fight champion, with ease. Based on Gouketsu's own experience, no beings on Earth are stronger than him. Considering that Gouketsu proclaimed Orochi to be stronger than any other beings in the world while as a Dragon-level monster and taking his own arrogance into account, it can be speculated that the "Monster King" is at the very least at the level of monsters who exceed the usual Dragon-level, like Boros and Awakened Garou or possibly above them.

Physical Abilities
Monster Cell Generation: While it has yet to be seen, Orochi apparently has the ability to create as many of Mysterious Beings as he wants. His body seems to be able to create Monster Cells, which in turn transforms humans into monsters upon consumption.

Limb Extension: Orochi can apparently extend his limbs or at least his horns over long distances.

Trivia

 * The name "Orochi" (大蛇) literally means "great snake".
 * Orochi is the sixth of many "Kings" mentioned in the series, the others being the Subterranean King, the Beast King, the Deep Sea King, the Ancient King (anime-only), the Sky King, the King of the Underworld (anime-only), and the Forest King.
 * He is the 2nd king with a confirmed name, the 1st being Pluton, King of the Underworld.
 * Orochi is a manga-exclusive monster as he does not appear in the Original Webcomic, although his boney appearance is similar to God.