[Help] Building a Betrayal

[Legimus]

First time poster. I have never been a DM before, but I am hoping to for my group in the near future. I've looked through a lot of campaign modules, but I think that for my first experience I would really like to design my own world and keep it simple. My friends and I are far apart, so we play over video chat, and good dialogue is especially important to us (as I'm sure it is to a lot of people). I'm having trouble designing my main villain as a character, and I'm hoping to get some help coming up with ideas that will make my players feel like they have a personal connection, rather than just vanquishing the bad guy.

On the broad strokes, my campaign takes place in a kingdom that worships a pantheon of six gods. The gods are benevolent, and the kingdom has enjoyed generations of prosperity and peace under their guidance. It is split between six temple cities, with the temple to the chief god being the capitol. Importantly, the kingdom does not have a large military because it has been protected from invaders by the angelic army of their gods, led by an archangel who I'm calling Samael for now. This is my villain. For one reason or another, the angels are sent to defend the kingdom, but after winning find they cannot return home. The angels are trapped, and the gods fall silent. At first, they are quiet guests, but some of the angels start to grow restless. Samael, the gods' most loyal servant, becomes increasingly agitated. First, he worries that it was something he or his angels did, but he can find no flaws in his kin. He turns to the mortals, knowing that they are favored by the gods, and implores them to contact the pantheon, but the gods are ignoring the mortals too. As Samael grows obsessed with getting home, he coaxes and then begins outright forcing the mortals to devote more time to trying to please the gods. The kingdom becomes a brutal theocracy, with Samael and his angels forcing everyone to fervently worship gods that do not answer. Eventually Samael snaps, rationalizes that he was trapped here to punish the mortals, and begins massacring everyone he deems impure.

My plan is for the players to play through all of this. I want them to be personally familiar with Samael from a very early moment. Around the first half of the campaign will be devoted to looking for the gods (so to speak), but I want them to get progressively more worried about Samael, and I want them to feel actually betrayed when it becomes clear that he needs to be stopped. I figure that the best way to do this is to give them a positive relationship with him and the angels at first. I'm having trouble crafting this, though. Do you all have any ideas for:

Ways to introduce someone as powerful as an archangel?
Positive first experiences?
Things that will be necessary to build trust?

Samael is supposed to be a legend among the people, and I want him to be a friend and a hero to my players. I want my players to really feel his descent into madness, and I want them to feel affected by his betrayal. I would love any advice on how to build this sort of relationship with a NPC. I'm open to both general principles and specific suggestions about events that could/should happen in the campaign.

Thanks!

[Zman]

Firstly, I like what you're planning so far and have a couple of suggestions.

First, snapping and massacring people is a bit much and I think you have more room for shades of grey. What if it ends up being punishing the impure, but takes on the scope of the Salem witch trials. Samuel is judge, jury, and executioner. The final straw might be when he puts a beloved npc, friend and ally on trial and will of course execute him. Let the party discover there is a 100% conviction rate and all were executions. When the party resists, let Samuel order their arrest and put one or all of them on trial.

As for letting the party know just how powerful Samel is, let the party rise to defend the realm from attack, make it ugly. Let the party rush headlong into the jaws of the enemy assault, toward the leader. Massacre the human forces, push the party to the brink, put half or more of them on the ground, let them roll death saving throws, and when it looks hopeless and like a total party kill have sameal and his warriors arrive in a blinding flash of angelic glory, let Sameal personally save them, but have let him almost ignore them as he moves on to more pressing matters. Let the party watch him obliterate the threat that just nearly killed them(and if the dice go poorly killed one of them).

Portray Sameal as nigh all powerful at first, then once cut off show his more human side, show his deep seated and hidden fear of being alone. Show a paranoia. Show a made up fear of losing their celestial powers. Let the blame for humans start to show, maybe a quest about an evil wizard or cleric who could be to blame(they are innocent, but Samael's mistrust and quick reaction to blame humans creeps in).

That's how I'd do it. Sameal goes from all powerful savior, to noble leader, to putting on a good face, to mistrusting those around him, to the edges of paranoia, to authoritarian zealous wrath, then he is judge, jury, and executioner of those close to the party. Then let Sameal put one of the party on trial.

Maybe Samael even gets to the point he puts a fellow angel on trial and attempts to absorb their celestial power, maybe he has a theory that alone they are not strong enough to breach the planes and contact the gods, but if one of them were more powerful they could. As the strongest, it is his burden to bare, his duty. He is only trying to do what is right. But, he is lost, lost and afraid and terrified to accept his new existence.

[Jallorn]

As for letting the party know just how powerful Samel is, let the party rise to defend the realm from attack, make it ugly. Let the party rush headlong into the jaws of the enemy assault, toward the leader. Massacre the human forces, push the party to the brink, put half or more of them on the ground, let them roll death saving throws, and when it looks hopeless and like a total party kill have sameal and his warriors arrive in a blinding flash of angelic glory, let Sameal personally save them, but have let him almost ignore them as he moves on to more pressing matters. Let the party watch him obliterate the threat that just nearly killed them(and if the dice go poorly killed one of them).

This could be a bad idea. It could work, but I worry about the players going, "Oh, great this is just a chance to show off how powerful this guy is." A far better idea would be to do it the other way around. Have Samael easily dispose of an enemy, but in a way that allows that enemy to escape. Maybe he doesn't even have to fight, the guy just goes, "Oh crud, Samael," and runs. Then, later, have the players fight this guy and make him a really tough fight, like, possibly takes out a party member hard. Then, the players can put two and two together and go, "If that guy was so bad, but he was terrified of Samael..."