King Ghidorah is a three-headed dragon and a Space Kaiju known throughout history as The King of Terror. 65 million years ago, he and DesGhidorah came to Terra and caused the KT Extinction before being driven away by the Eight Guardians of Terra. He is also known for being the arch-nemesis of the King of the Monsters, Godzilla.
King Ghidorah has an incredibly muscular build that is covered in bright golden scales and while he lacks arms, he has two massive wings that allow him to fly at incredible speeds that defy his size. He also has muscular legs with sharp clawed toes and two tails that are each tipped with a flat, paddle-like protrusion that are covered in spikes.
His most distinctive (and iconic) feature though are his three heads that are held by long, thick, serpentine necks. The horns on all three of his heads are similar to that of his relative, Mecha-King Ghidorah. In the past, each head had a mane of fur but over the years, the hair has now disappeared.
King Ghidorah has across countless decades demonstrated almost nothing but malice, homicidal apathy, and equally destructive disregard for mortal life, sentient or not. Extremely few beings have earned anything but his disdain, mostly a begrudging respect on account of their power. His only desire in life is to gain power, travelling from planet to planet and absorb the souls of their inhabitants in order to became more powerfull, bringing countless of alien species to extinction or even to the brink of, even with his own kind.
Most of King Ghidorah's past is shrouded in mystery, but it is believed that millions of years ago, King Ghidorah was but one of an entire species of space dragons that traveled to different planets across the known universe in order to colonize them and preserve their species. However, at some point, King Ghidorah became corrupt with power and immortality and killed off his entire species (With the exception of Guardian King Ghidorah) in order to become more powerful and to keep himself alive forever.
At some point after wiping out an entire civilization on Venus, he encountered his younger brother, DesGhidorah, and the two joined forces to attack Terra together, where they caused the KT Extinction before being stopped by the guardian Kaiju: The Eight Guardians of Terra. King Ghidorah barely survived the battle and was forced into retreat, while DesGhidorah was sealed beneath Infant Island by Gigamoth before he could flee. Then at some point after, he traveled to the Cryog home world and completely destroyed it, leaving the Cryogs on the brink of extinction, before encountering Gigan.
Half-Century War Arc
King Ghidorah and Gigan were drawn to Terra from the edge of the Solar System when Dr. Deverichs ultra-powered Psionic Transmitter was used to summon SpaceGodzilla. In 2001, the two made landfall on Terra and began to cause mass destruction to every human city they came across. At some point, the two were attacked by Mothra and Battra, but were able to defeat them, with King Ghidorah being able to mortally wound Battra. The duo also came across Anguirus and defeated him as well. A year later, King Ghidorah and Gigan were lured to Antarctica where they encountered Godzilla and were able to briefly overpower him until Ota Murakami arrived in control of Kiryu. The two groups were both evenly matched until the two Space Kaiju were struck by a blast from Dimension Tide and King Ghidorah was never seen again.
Post-Trilopod War Arc
While King Ghidorah himself doesn't appear, he appears in Godzilla's memories as the Shobijin show the core members of Fairy Tail Fairy Tail after the Earth Defenders were transported to Earth Land. As the Fairy Tail mages witness Godzilla's memories, they see King Ghidorah in his battle against Godzilla and Kiryu.
Tenrou Island Arc
Again, while King Ghidorah himself doesn't appear in the story, the Shobijin talk about him to Mirajane Strauss and Lisanna Strauss. As they are explaining Mothra and Battra's ancestry, they tell the Strauss Sisters about how King Ghidorah and DesGhidorah invaded Terra and caused the CT Extinction and they were defeated by The Eight Guardian of Terra.
Gravity Beams: King Ghidorah's signature attack, from his mouths King Ghidorah can fire golden lightning bolt-like gravity beams. These beams rival Godzilla's Atomic Roar in power, and are capable of causing large-scale explosions. He used them during his battle with Godzilla and Kiryu.
Scale Beam Barrier: King Ghidorah’s scales work to distribute the force of energy and impact of beam attacks across his body. This makes punching through his scales with energy projectiles all but impossible to anything except overwhelming force or condensed rays specifically made for cutting.
Gravity Mastery: King Ghidorah’s core power is gravity alteration, being able to both shut off, intensify, and redirect the flow of gravity between matter. This, in essence, gives him both matter alteration and telekinetic powers, able to lift, reshape, and set matter around him. This can vary from assembling himself a throne out of debris fields to pulling something closer to him. The most extreme example is, after a lengthy charge time, sending out a massive wave of graviton particles that drastically increase the gravitational attraction between everything around him and the ground. If done to another Kaiju, this can knock them to the ground and pin them down. If done in the middle of a city, it would cause all the buildings to be pulverized under their own weight and the less said about the lifeforms within them the better.
Flight: Being a dragon, King Ghidorah posses massive wings which he can use to flight at Mach 3 speeds in Terra's atmosphere and as well as in the vacuum of space itself. This allows to gain the aerial advantage when in combat with other kaiju. And by flapping his wings, King Ghidorah can create great winds to blow opponents away.
Immense Strength: Despite a lack of arms, King Ghidorah possess great strength. With his powerful jaws, he is capable of biting Godzilla and lifting him off the ground. He possesses quite possibly the greatest strength of any Kaiju Godzilla has ever faced, having enough sheer power to toss around smaller Kaiju like rag dolls.
Immense Durability: King Ghidorah is insanely durable. His scale mesh is resistant to both blunt force trauma, edged and stabbing attacks, extreme temperatures, and energy projectiles. He is one of the few enemies that can almost completely resist a blow from Godzilla's Atomic Breath. The only means of piercing it is a concentrated, prolonged attack on one spot in particular; a very difficult feat in the midst of battle with him.
Enhanced Speed: Despite his massive size, being bigger than Godzilla himself, King Ghidorah can be extremely fast in the air. He is even faster in outer space.
Enhanced Endurance: He can be wounded, he can be impeded, he can be fighting for days, but Ghidorah does not tire easy. This is an entity that persists off the life force of others, and with thousands of millions of souls trapped inside him, it takes a lot to make him start running low on power.
Physiology: King Ghidorah’s internal biology is just bizarre. He lacks most vital organs or any equivalent to. Blows to the head do not greatly daze or damage him because none of his three heads have brains. The core, a crystalline sphere structure deep inside the chest cavity, seems to function both as a brain and heart. This is quite possibly his only vital area but even so, hitting it is extremely hard given it’s both extremely durable and covered up by a dozen meters of tough scales, hide, and muscle.