get ready for some Zarkangst !
This is my own headcanon of Zarkon’s past, where Alteans are dick and Galras are pure so if you don’t like it, don’t fucking read it ! (but let me tell you you’re missing on a good headcanon) Also, it’s written like a fic, so enjoy the angst under the cut and don’t hesitate to use my hc and discuss it with me !
Alteans are shaped like humans, even if they are way stronger than them. They are not shaped for survival : they are small, thin, and bright colored hair and markings doesn’t look very effective camouflage in an evironement of green plains and open space. It means that their planet must have been pretty much peaceful without a lot of predators but lots of resources and food. That is one of the main reason why alteans could evolve faster than other species: they didn't have to think about survival.
On the other hand, galras are build for survival: they are tall, have dark skin, they have wide shoulder and long legs, feline nose, wide eyes, large ears, claws, they are fast and strong: they have evolved to survive. It's most likely that they were hunted by predators on their mother planet. They are a proud species because they are able to fight against any animal that want to eat them, and that from a young age. But when you're fighting to survive, you can't create space ships and things like that.
When alteans discovered their planet, galra were evolved quite a bit: they had a language, cities and a bit of technology but they were far from being as evolved as alteans. The alteans spent a bit of time with the galra, learning about their customs and how they lived, learning their langage as they always did when they discovered a new species. They also gave them advanced technologies and because galras were smart, quick to learn and curious, because when you're hunted you develop these capacities first, they took a grip of the tech quickly. Alteans offered them to come to the planet Altea if they wanted to learn more about technology and other civilisations. A lot of galras accepted and were were completely overthrown by this society when they got on Altea: they discovered how different their society was, how weird it felt to live without thinking about not being eaten, how wide the universe is and how amazing it can be.
But alteans could be haughty and arrogant: they lived surrounded by high tech, and they were one of the smartest species to exist with the Olkairi so when galras came in the universities to learn and they had little to no knowledge about anything, it wasn’t rare for alteans to make fun of them. Only the ones who went on the galra homeplanet really knew about galras and how amazing of a species they were, the other alteans showed no interest in them at all so the galras never tried to teach them. Alteans kept making fun of galras, even if it could be considered hurtless and jokes but days after days, months after months, galras didn’t find it kind at all. More and more galra starting to hate alteans all together and they'd pick fights and insults alteans who looked down on them. They could hurt alteans fairly easily and even if most of the times fights were called off before anyone could get seriously hurt, there were still a few dead bodies and deep wounds. Alteans were now afraid of how dangerous and untrustworthy galras were.
Zarkon was one of the head chief son. Zarkon had heard about Altea and how wonderful it was, he wanted to go there to learn and enable his species to continue growing. Even if he knew about how hard it was to be a galra on Altea, he still wanted to see how it looked like. He was welcomed by the king of Altea just like any royalty would have been welcomed. He saw the nasty looks shot his way, he heard the whispers of the people, but he took it on himself and didn't react because he was the closest thing to galra royalty on altea: he was the face of his people. So he sat through it with a smile.
Zarkon had a friend, an ally in this hateful environnement: prince Alfor. He had met him at the welcoming ceremony and he was one of the very few nice altean to him: he wanted to learn more about galra society and he helped Zarkon to learn the basics that every Altean kid knew without looking down on him, not even once. Alfor never distanced himself from him even when Alteans were clearly against Zarkon staying with the royal family in the castle. And while they looked like friends to the people, they were becoming way closer than just friends when no one could see them.
One day, Zarkon came back on Altea from his homeplanet to discover that Alfor was now the king. Zarkon was happy for him of course, ahe didn’t mind as long as they were still able to live their love somehow. When Alfor married to an Altean duchesse, Zarkon stayed quiet since Alfor loved him. Alfor told him about his crazy dream: building the most powerful weapon ever, Voltron, a giant robot made up of 5 lions piloted by 5 paladins. He wanted to create a robot that was almost alive. Zarkon wanted to help him as much as he could: he brought him to his homeplanet to show him one of the satelites that could be used to create the quintessence. Alfor destroyed the planet, Zarkon didn't say anything. Alfor loved him and that's all that mattered.
When the lions were finished, Zarkon was the fist one to see them. They were such magnificent beasts, he would have killed to pilot one of them. Needless to say he had no hope Alfor would let him pilot one of them. But Alfor offered him the black lion. The black lion had chosen him. Of course, alteans weren't happy with that: galras cannot be trusted. A female galra piloted the red lion, keith's mom, and the other 3 lions were piloted by alteans: Haggar was the blue paladin, Alfor was the yellow paladin and a random altean was the green paladin.
Zarkon had to work twice as hard as the other paladins to show his worth to the altean people: he worked to get the strongest bond possible with his lion, he worked to be the strongest of them all, he worked to be the best paladin and leader he could be. As the leader, Zarkon was the one alteans blamed everytime something went wrong: that's when he started to lose it, when he realized nothing would ever be enough for the altean people. Nothing he did was enough to prove his worth. He was always the one at fault. It was always his fault. Zarkon became reckless: he needed to be better, to be smarter, to be stronger. His bottled up feelings started to resurface, slowly shifting from sadness, loneliness, pain, dullness towards anger. He didn't tell anyone, not even Alfor. Alfor who was starting to distance himself from Zarkon to attend to his people and his family. But he still loved him.
Zarkon didn't talk to people: the engineers were afraid of him, the staff of the castle was scared of him, even the green paladin was against him. The red paladin was turning against him as well: she noticed the impact Zarkon's actions had on the people and she saw how unpredictible Zarkon was. Haggar was on Zarkon's side, she knew how bad alteans treated galras. They got somewhat close when they started to work together but he never opened up to her. She saw what the alteans were doing to him, to his sanity and she started hating them for it even more with every day passing. She hated herself for being of the same kind as those hurting Zarkon.
Alfor was spending less and less with Zarkon, they only saw each other during missions. He wasn’t whispering sweet loving words in Zarkon’s ear anymore. He wasn’t giggling when Zarkon kissed him anymore. Because he wasn’t standing by Zarkon’s side anymore. He was with his family, his wife who has always hated him, his daughter who hated him as well. He was with his people, who hated him. But he was still in love with him, wasn’t he ?
The racism towards galra was only getting more and more agressive, to the point galras couldn't even live on Altea anymore. Altean wanted him and the red paladin to step down from their lions. But Zarkon refused. He was the only one who could command the black lion. He had been chosen by Alfor because Alfor trusted and loved him. And Alfor still loved and trusted him. Despite what everyone else was saying, he knew he was worthy of the black lion and Alfor's trust. He would never give up on the black lion.
But after one mission during which Zarkon almost got them all killed, Alfor had to take a decision: he asked Zarkon to give up on the black lion. Zarkon’s whole world shattered at that. It wasn’t a question. It wasn’t a friend trying to help a friend. It wasn’t a lover attending to his beloved. No, it was an order. Zarkon refused, and Alfor locked the black lion away from him. Alfor didn’t trust him. Alfor didn’t love him. Alfor didn’t love him. Alfor hated him. Alfor was just like the other Alteans. Alfor wasn’t any different from other Alteans.
Zarkon couldn’t feel anything but anger. He wanted revenge. He wanted to kill the man who betrayed him. he wanted to destroy the species that hated him for no reason. He needed revenge. And up to this day, he still can't feel anything but anger and a thirst for revenge.