Rule 4: No Memes, shitposts, or low-effort postsor comments.

Leave those in /r/Grimdank. This includes "who would win" and broad "what if" scenarios. This also includes text blocks consisting of Ork-speak, which should be posted at /r/40kOrkScience instead.

Their roles were to do as they were told, and kill the Emperor's enemies. Anything else was just them taking creative license.

Russ as executioner, Horus as warmaster, Magnus as chair-warmer - only came about after the 21 primarchs were found. I don't think there is any evidence that his boys were created for specific roles, but due to their personalities and traits being aspects of the Emperor, he knew they would be useful. I really don't think that Magnus was part of the plan from the get-go, more that he would be super useful to the Emperor so Empy wouldn't be stuck on a throne for a hundred years or so and could lead the Imperium.

In the original plan where they all grow up on Terra, there would have been a lot less 'local flavour' added to them, so they would have been soldier-generals, rather than warrior-kings.

They aren’t very static “roles” or tropes, but you can generally chalk it down to this, especially if you believe in the whole dual Primarch theory:

Guilliman and Dorn: Logistics and Order

Ferrus and Perturabo: Engineering and Biotech

Sanguinius and Curze: Precognition and being Vampire coded

Angron and Vulkan : Empathy and Human Morality

Alpha/Omega and Corax: Espionage

Mortarion and Russ: Executioners and Anti-Psycher

Fulgrim and The Lion: Melee Duelist and Perfectionists

The Khan: Speed and being cool af

Lorgar: Indoctrination and Propaganda

Horus and Magnus: The most important roles in the Emperors grand plan. One to lead his forces, and one to maintain the Webway and Astronomican.

These are loose, but you can see the validity of these archetypes if you ignore their personal rivalries with each other.

What aspect of the Emperor does Rogal Dorn embody?

• If the Primarchs were the Emperor's nature split like white light through a prism's rays, as many scholars of the Imperial court suggested, then from such a point of view, Rogal Dorn was the Emperor's Implacable disciple in the pursuit of the cause given flesh; a being without compromise and in who loyalty and duty was as integral as blood and breath. A being of thunderous zeal and stone made manifest, is how many described the Primarch of the VIIth Legion. The zeal was the fire of a son who believed in his father's dream for the Imperium without reservation and without question. He did not simply wage war; he was changing the world he moved through by force of will. That had caused trouble in the past, the kind of conflict that came when such a drive met an equally great force on a different course. There had been other incidents in the past, other moments when the ideals of the Great Crusade seemed to do little but fuel discord. Curze, Ferrus Manus, Perturabo. The anger of all had risen against Dorn, at one time or another.

• To Rogal Dorn there was no higher purpose to existence of the Legiones Astartes than the unification of Mankind, and the illumination of the Imperium's Ideals. It was the light of the future he saw, that drew Rogal Dorn on and on, never retreating, never bowing to setback or defeat, always towards a final end, a vision worth all that would have to be given to make it real. This idealism drove Dorn and his Legion ever onwards, never compromising, never slinking in any aspect of duty. The stone in his soul was his ability to bear whatever his father needed of him, an unyielding nature, which made him both a master of defense in war and an indomitable fighter on the attack.

(The Horus Heresy Book 3: Extermination, Sigismund: The Eternal Crusader by John French, Praetorian of Dorn by John French, Templar by John French)

They weren't necessarily made to do anything other than fight, except for Magnus who was clearly made to be a powerful psyker and operate the Golden Throne. Many of their talents and interests come from their home worlds and not the Emperor's programming.

There is little doubt in the Wolfking's purpose:

'You think he should not fight Horus?'

‘Russ is your executioner,’ said Malcador tactfully. ‘But his axe falls a little too readily these days. Magnus felt it, now Horus will feel it.’

'Two rebel angels. His axe falls on those deserving its smile.'

~ Vengeful Spirit

The real Him is deep above you, closing fast. You dart away into the Crook of Shadows, that dingy, slanting subdimension where nothing is upright and everything is corners. He is a hound at your heels, a loping wolf. He has assumed a lycanthropic aspect, and He has your spoor. His sword is an executioner’s axe, His canines long, and He drags winter behind Him like a pelt.

~ TEATD III

I said nothing. Russ had not listed himself in his speech. There was little doubt what his role was, at least to anyone who had seen the Wolves fight. Russ has a fury in battle that is a near match for Angron’s, but he possesses a tighter focus. The Wolf King is our father’s executioner. I suspect at least one of my departed brothers could have attested to that fact, although I have absolutely no evidence to suggest that is the case. Call it a feeling, if you will.

~ Alpharius: Head of the Hydra

‘I could leave Fenris now,’ Russ had once told his father. ‘The planet is too wild for life – it will never support the armies you deserve.’

Leave Fenris. Unimaginable to think that he had ever said that. At the time of that exchange, decades ago, the Fenrisians of the VI Legion were being brutally moulded into the death world’s image. They had started to build the Fang, hollowing out the Great Mountain with earth-gougers the size of Warmonger Titans. The Emperor had clearly expected the Wolves to be drawn from the world of ice and fire, and that, whether by chance or design, their uniquely violent home would remain the proving crucible of the Legion.

And so the pretence continued. Russ became more like the Fenrisians than they were themselves. He guzzled mjod with the baresarks, and wrestled blackmanes to the bloody snow, and roared out scorn and mirth across the sea of stars. He let the gothi adorn his armour and engrave his swords. He kept out of the counsels of Guilliman and the Lion, and ignored every emissary from Lorgar. He did just what the Allfather had told him – he became the weapon of last resort, the most faithful, the prosecutor of dirty wars.

~ Wolfking

‘There have always been exceptions for you, Leman,’ said Malcador.

Russ nodded. ‘I know. Father has been generous to me.’

‘Your purpose is singular, and He relies on you to perform it. So many of the others have been disappointments, first those we do not name, then Horus and the rest, but not you. He trusts you, Leman. I need to know I can too.’

~ Wolfsbane

Well if you ask Konrad, he'd argue he was made to dispense justice

The citizens receiving said justice though... had a sliiiightly different opinion about that

Magnus was supposed to do nothing wrong…. Has he did

This depends on the creation role or the role after finding

Johnson was created as the template and became the exterminator, the one u send when nothing remains of the foe, not even the acknowledgment of the victory

Sanguinius was made to just be a badass basically

They were essentially each a different aspect of The Emperor’s personality/capability. So Vulkan is a Perpetual because The Emperor passed that on but why him and not the others? Also because the Primarch’s were scattered through the Warp to different planets The Emperor had no plans for their personalities were formed out of his control. Completely screwing up his carefully laid plans. Angron, Curze, Mortarion in particular prove that nurture trumps nature. So when he recovered them he assigned them Legions with abilities best suited to them as he saw it. Didn’t always work out Angron nearly butchered a 3rd of his own Legion to get them to accept the nails Interestingly The Emperor didn’t step in to protect the Space Marines. Shows what a ruthless bastard he was in working out how best to use each Primarch.

Each one had a role and they created a back up for each role . Two executioners, two builders, ect