History of The Enlightened One

About five hundred years ago a man later called the betrayer by Earth and "The Enlightened One" by his people had a knack for technology and advanced science further in his time than thought possible.
But he did not make weapons, knowing that earth's governments would use them to try and subjugate the world and the world would be destroyed.

So the UN tried to make him to comply by force, he responded by building a ship and left into space with several million people. His technology, so advanced was it from what now exists that no one but he could maintain because he took/destroyed all the knowledge of how with him, because he feared that someone would make weapons with it

But he left one thing behind

He left a vault, supposedly a vault containing all the knowledge he had uncovered, for two hundred years scientists tried to open the door leading inside but it was protected by a computer program so advanced that it had a conversation with the person wanting access and could see through deception the program displayed itself as a hologram in the same form as the enlightened one.

Three hundred more years passed of wars and devastation, so much so that technology had only advanced little compared to when the enlightened one left (advanced little as a whole it had gone up and down a lot but overall only slightly more advanced).

When a young woman found the vault quite by accident and through begging and pleading achieved access to the inside where she discovered that the hologram was never a hologram but the enlightened one himself.

He had been sending transmission to the vault and communicating with the people, she begged for him to return and stop the world from destroying itself, how it had nearly done several times before, he agreed
but it was a trap, she had been sent to lure him into a trap, the people thinking they could subdue him and take his technology for themselves but he saw through the lies and was prepared with a surprise.

But he returned and his ship received heavy damage, as they had more advanced technology then he thought they would, as they send the assault vessels to board his ship the rest of his fleet arrived.

All of Earth surrenders at the sight of it except one nation, the USA, the nation that had instigated his return and tried to force him to surrender.
After trying to reason with them he sends his soldiers to attack and occupy LA, after fierce fighting and even some losses he wins, but they don't give up.
Instead they kill the family of the young woman who told him of the trap (the same girl that opened the vault) and in retaliation he destroyed the entire city of Washington DC.
Awed by the power to destroy a city from orbit with no chance to retaliate the nation gives in.

It has been one year since that time. The Enlightened One has left and one of his generals and one of his armies remains. Earth's occupants have taken it well for the most part with incidents only occurring from radical groups. Now the invaders have posted up recruitment signs, inviting anyone who wishes permission to enlist and join The Enlightened Army.

(So I changed the idea slightly, basically you need to be a recruit for the army, this doesn't mean you have to know how to fight or even want to fight. You can make up reasons/benefits they are giving out to people who join them. FYI they haven't freely handed out the technology they possess as they do not yet trust those of earth and that can have something to do with your reason. Perhaps giving incentives to those recruited like curing their families of all disease and illnesses or stuff like that.

Go ahead and post before me a little about your character maybe even an intro to the training program if you get to it before I do.)