Evil character played off as troubled morality

[u/throw_away_2910]

Hello!

I am currently running a D&D campaign, with heavy themes of good vs. evil and grey morality and all of that. One of the main drivers of the plot are the actions of a doomsday cult that is summoning demons all over the place and hopes to usher in a demonic invasion to take over the world. One of my NPCs that has a pretty big impact on the story (he summoned a bunch of demons in a place that they were at, killing a bunch of innocent people but also going out of his way to free the party from being killed or otherwise by a bunch of guards) is part of this cult, and a lot higher up in it that he lets on. However, he's tagged himself along with the party for a while.

Off-screen, he and another PC (who had to take a break for a few weeks, so I wrote him out of a few sessions) went on a DOOM-style rampage against members of the cult. Since "joining" the party, he has killed or had a very distinct part in killing two other members of the cult. Another PC has had a vision and recitation by a certain demon burned into their brain, and this guy told the recitation back word-for-word.

Basically, the party KNOWS he is involved in the cult in some way, but he is also going out of his way to kill members of the cult. In actuality he is trying to gain the trust of the party for other things down the line (none good), so far with varying success. One character (the one who had the vision) specifically wants to kill him; another (the one who killed a bunch of cult members off-screen with him) is alright with him. Most of the party is generally indifferent towards him, and one of my players out of character has speculated that he seems to have a very conflicting morality.

In our next upcoming session, he is going to try and help the party kill our first major boss (leader of the cult) and stop him from summoning what is effectively just Satan, and I'm hoping that gives him a little credibility.

Truth be told, the guy is basically pure evil. However, he also has no qualms with things like lying and dishonesty to convince the party that he's good. In other words, he's a wolf in sheep's clothing, and I want to make him look as much like a sheep as a possibly could. So how do I develop him to make him seem more morally grey and complex? How do I have him lie to the party to make him seem trustworthy? Is this really doable?

[u/Maniachi]

Why does he have to be pure evil?

[u/throw_away_2910 → u/Maniachi]

What do you mean? He is because that's the kind of character he is.

[u/Maniachi → u/throw_away_2910]

But he doesn't have to be. Your player is angling that they see him as someone morally complex. Why fake that and not actually make him morally complex? Why are you stuck on him having to be evil, and then trying to trick your players into thinking he is morally complex? It makes no sense to me. Either make him morally complex, or allow your players to pick up on the fact that he is irredeemably evil.

[u/throw_away_2910 → u/Maniachi]

I mean, I could, but this guy is a member of the doomsday death cult. Kind of the whole purpose of why he's trying to weasel is way in and make it seem like he's complex is because I'm hoping to try and have him manipulate the party later on into doing things that he wants if things work out in such a way. To do that, I'd like to have him seem more complex than that when in reality he's just gaining their trust so he can use it for his own purposes later on.