The Ghidorahs are a species of extraterrestrial three-headed dragons who are known to destroy planets, lifeforms inhabitants, and civilization. They were all created by the deity known as Gidrah, The Planet Eater who is a god to the Exifs, they destroy and spread chaos due to the fact that it in another dimension. Gidrah's progeny became threats to many worlds like the Nebulans and the Cryogs, scene as weapons by the many aliens races, and are consider gods to the Exifs and humans.

Earth became a target for Gidrah which led it to create the first Ghidorah known as Cretaceous Ghidorah but the world is protected by Devine Moths known as Mothras which led to a war between the two species.

Gidrah and the Ghidorahs nature is that they have an infinity for lightning and electricity due to their biology known as the Ghidorah Force and they alter the weather around them due to not being part of the natural order of a planet which they spread destruction, each Ghidorah were given unique abilities.

Gidrah have created many Ghidorahs but there are only five left alive as part of the first generation which Ghidrah will produce more which take billions of years

Gidrah
Gidrah is the God of the Exifs and progenitor to the Ghidorahs, it have been in the universe via other dimension for countless millenniums. It is an intelligent being who guide the Exifs to planets to inserts their religion while leading Ghidorahs to destroy planets, it very intangible when it was summon due to being like a shadow as it not effect the our laws of physics when it connected to its priest. Gidrah (Gē-drə) produce Ghidorahs by unleashing energy spores from it body as they are created similar to a star. Gidrah being an energy-based lifeform have no gender but many see it as male as it was given title like the All-father of the Ghidorahs, King of the Void, and Golden King while it priests such as Metphies see it as a female as they invision it as a beautiful woman. It have a total length of 20 kilometers. Gidrah is originally from Godzilla: The Planet Eater as that version of King Ghidorah.

Cretaceous/ Grand King Ghidorah
The 1st Ghidorah to be created and arrived on Earth approximately 130 millions years ago in the Cretaceous period but was defeated by Primitive Mothras and sealed him in the Gulf of Mexico where he change into Grand King Ghidorah. He originally stand 60 meters tall, a wingspan of 80 meters, and weigh 50,000 tons in the Cretaceous but stand 150 meters, have a wingspan of 175 meters, and weigh 80,000 tons. This Ghidorah is from Rebirth of Mothra 3. He is unique as he took a very small form in the Cretaceous but grew large for the whole time he was sealed.

Desghidorah
The 2nd Ghidorah who arrived on Earth, he had destroy the civilization of Mars 65 million years old, he was defeated by defeated by the devine moths as he was sealed in the the Hokkaido. He stand 50 meters tall, have a length of 100 meters, weigh 75,000 tons, and have an 80 meters wingspan. This Ghidorah is Rebirth of Mothra. He is unique as most Ghidorahs have lightning-based breath but this one breathe fire and have a more demonic appearance.

Gorath/ Monster X/ Keizer Ghidorah
The 3rd Ghidorah who arrived on Earth, he had visited the Space Hunter M 12,000 years ago as he slaughter many space dinosaur but one of them were modified into Gigan as he fight him countless of time as Gigan is being modified in each retreat until Monster X retreat, he landed on Earth but was almost defeated by Battra. As Monster X he is 80 meters tall and weigh 60,000 tons then as his true Keizer Ghidorah form he is 140 meters tall, have a 200 meters length, and weigh 100,000 tons. This Ghidorah is from Godzilla: Final Wars. He is unique as he have a skeletal-like monster form then transform into a true Ghidorah, he also able to travel as meteor called Gorath and unique horn patterns.

King Ghidorah a.k.a Monster Zero
The 4th Ghidorah who arrived on Earth, he had destroy the civilization of Venus 5,000 years ago which some natives escape, he fought the devine moths but they easily defeated him and seal him in Antarctica. He stand 110 meters tall, have a wingspan of 175 meters, and weigh 70,000 tons. King Ghidorah is a combination of the Showa version in design and the MonsterVerse in location and personality. He is unique that each of his three heads have there very own personalities (Ichi, Ni, & Kevin) unlike the rest of his kind, making him the black sheep of kind.

Ghidorah/ Emperor Ghidorah
The last and youngest Ghidorah who arrived on Earth as arrived in ancient Japan but unlike the rest of his kind, he see the beauty of the planet as he become a Guardian along with a Mothra and a Baragon, he was in hibernation in the Suicide Forest until he meet his family. He stand 50 meters tall, have a wingspan of 93 meters, and weigh 25,000 tons but his adult form is 158.8 meters tall and weigh 141,056 tons. This Ghidorah is basically the GMK King Ghidorah with the origin of his Kingdom of Monster counterpart and his final adult form is the MonsterVerse King Ghidorah without the different personality. He is unique due to him starting that he is a gentle giant and respect the natural order unlike the rest of his brethrens.

King Ghidorah II/ Mecha-King Ghidorah
A clone of the original King Ghidorah created by the Garogas in hope of using their own Ghidorah to destroy their enemy Zone Fighter, they have to wait for the Dorats to mutated in 1940s but lose it as it become a weapon for humanity. It Dorats forms is 30 cm tall and weigh 0.8 kg, it combines form is 100 meters tall, weigh 40,000 tons, and have a wingspan of 150 meters, his cyborg form have the same height and wingspan but weigh 40,000 tons. This is basically the Heisei King Ghidorah with his origin of being clone of King Ghidorah from the novelization of GvKG and the possible origin from Zone Fighter as a creation of the Garogas which is not proven in the canon Showa series.

Nebulae Ghidorahs
They are the same of newborn Ghidorahs who are created from the energy spores of Gidrah similar to how starts are being born and will take time to create them.

Bonus
In the Aftermath series, King Ghidorah was revived by Metphies into secret as a human size Ghidorah along with many monsters, he have a body of the Heisei version but each heads have their own design: Ichi have the Heisei design, Ni have the Showa design, and Kevin have the GMK design. When Gidrah was defeated and Metphies thought to be dead, they become minor criminals until they were try to be nice and turn over a new leaf

After a fight with the revived Keizer Ghidorah and almost killing King Ghidorah, Jumba was able to save them by fixing and healing them: Ichi now have a MonsterVerse style body, Ni have a prosauropod/ hadrosaur-like body, and Kevin have a Mushu-like body. They also gain love interests, Ichi have Mt. Lady from My Hero Academia, Ni have Ilia Amitola from RWBY, and Kevin have Gigabolt Man-O-War from Megaman X as they learn to have new lives.

After Ichi return from his Dark Ghidorah persona, he was given a MonsterVerse style head and a scar from Gidrah itself to symbolize him as a traitor.

Despite this Ichi remain with his friends Storm Eagle and Depth Charge, still caring to his girlfriend Mt. Lady and adopted kids Toga and Dabi, and still one of Cinos' best allies.