Name: Primarch Ronan Belleza

Titles: Lord of Eagle, Lord of Thunder, The First Born, the First Son, the Proto-Primarch, Primarch Zero, The Eldest Son

Legion: The Thunder Legion (Thunder Warriors)

Height 18 Ft tall

Black Hair Blue Eyes

Like the Other Primarchs, he is Extremely Powerfully Built powerhouse and Handsome

He is the Strongest in Terms of Physical Strenght and the Most Powerful Among his Brothers in terms of psychic powers so much so that Ronan could Challenge the Emperor if he Wants to

His Homeworld Called is Primordial

and Like Guilliman's Realm of Ultramar

he has his Own Realm

Guilliman has the 500 Worlds

But Ronan has 20,000 Worlds under his Rule and Rule Alone

And it is on Par with Ultramar in Terms of Prosperity

and it has some of the Religion from Old Terra still Intact as Ronan is very Tolerant in Religion Despite the Protess from the Minitorum

The Thunder Warrior Legion has never Broken up and Never been Purge in the Imperium, and their numbers have reach up to 1.5 Million

The Thunder Warriors are stable and have the Custodians and Astartes of their possessed of some impressive willpower and determination, as well as  hypno-indoctrinated mental safeguards

They are long Lived as well and Biological Immortal like the Custodes and Space marines

Meaning they will at their Prime

and they are still Stronger than the Primaris Marines

They will also have some of the Space marine Organs, as well the 3 additional organ much Early Due to their Primarch

Their Power Armor

Unlike in the Cannon 40k

Their Armor is Advance almost as much Near the level of Custudes with all the Necessary System of the Power Armor Needed

While some of the Elite have Access the Custodes Armor and Their Rare Terminator Armor

Mostly it from Ronan's Elite Preatorian Guards

Some of the Thunder Warriors in Rare Cases Some of them can Grow Taller and even More Stronger than the Standard Thunder Warriors So much so that, That even the Custodes are Tense and will try to Avoid not to Fight them

The Thunder Warriors have the Brotherly Kinship like their Younger Counterpart, they are brothers and can be Coordinates with themselves Making them more Dangerous than the Space Marine

They have all the Advance weaponry since it was gifted to them first

The Realm of Primordia

has at least 45 Forge Worlds (Moon and Asteroid Are not Included), and 250 Knight Worlds

And with Enough Agri-worlds to Feed the Entire Small Empire, and they have Tech to Harvest much Faster than the Standard Agri-world not just Faster but to Produced more food as well and they are able to store some of Ancient Terra's Food and Drinks

with at least hundreds of Titan Legions

Their Primary Forge World Kronos it is Larger than Mars itself and their Capability Surpass Mars itself so much so that the Mechinus from Mars demands them to Degrade it, which they Refuse

and all of them are loyal to Ronan alone and his Thunder Legion along with the Technology that Guarded them with jealous

They have a Flaw that is similar to Blood Angels Black Rage

It's Called Vengeful Rage

It's called that because of, Ronan's Lover has been killed before he is found by the Emperor

This Rage is Far Stronger than the Black Rage

Not only it Increasing the Strength of the Thunder Warrior, it also increase their Speed, their Toughness and even their Healing Factor as it Boosting even their Furnace (The Belisarious Furnace) to the point that they are almost impossible to be kill, because they constantly heal, unless you focus all of your firepower towards them 

and as well increasing their Librarians psyker Powers

Their Motto

Ancient and loyal forever.

From the stars we came, to the stars we rise

Ronan's Power Armor

(This is my Imagination) 

His Power Armor is the Best protection in the Imperium able to Rival the Emperor's Own Armor

His Weapons are

Flaming Sword: It was Forge by Ronan's Very own Hand, it's not just very powerful Force and Power Sword, Like the Emperor's Sword it can Permanent Kill a Demon

and Powerfist with Retractable Lightclaw with Combi Bolter attached to it and could fire as Fast as the Stormbolter

And his Flagship

It is called as the the Might of the Imperium

It can Carry Thunder Warriors up to 300,000

Crew, 400,000

Imperial Guard, 3,500,000 Soldiers

5,000 Adeptus Mechanicus Adeps

500 Titans

2,5000 Knights

It's size is 80 KM

It was Found in Their Primoria System by Ronan Himself 

The ship has been Exist Since the Dark Age of Technology

The ship in it's time is consider one of the powerful to have ever been created

it was automation and need smaller crew 

It has also an A.I 

It has it's own Small Factory that could Rival other Major Forge Worlds

(That far as i can Imagine)

That's all For now

This is will be another Universe

There is still alliaince 

but it will be only the Imperium, The Eldar and Necrons for now

The Tau will be there Enemy for a while

This is will be a cannon 40k

meaning the Legion has been broken

I Haven't Decided of which will be the starting

If it's Before or After Guilliman's Awakening

And Planning for a Crossover will be a Hard One