I'm currently involved in a really fun campaign with close friends and am running a PC with a troubled past. The character is Chaotic Neutral and has typically exhibited not entirely consistent characteristics: on the one hand, he's greedy, coarse and violent; on the other, he often stands up for those who can't stand up for themselves, who would be victimized (e.g., he might advocate for a wrongfully condemned man, or stay the hand of a friend ready to kill the last goblin as it begs for its life, etc.)
So far, I've tried to keep the PC fairly morally neutral; he gets along with the other PCs fairly well, and is happy to undertake quests (so long as the reward's good), but he has his own motivations and they aren't good, per se.
The GM has recently introduced some elements of my PC's backstory in such a way that enables, if not encourages, my PC to move into less morally ambiguous territory; whether this was the GM's intention in introducing these elements is unknown, but the result is that my PC's goals are now most likely evil, although the character likely doesn't see it that way. In some ways, I suppose, this is natural; isn't everybody a good guy in his own mind?
(And the goals of the PC will be pretty clearly questionable, arguably even to the PC: they involve enacting revenge on beings he at least philosophically knows are good-aligned, and potentially causing other mayhem, and he's prepared to do more or less anything, so long as it doesn't involve hurting those he considers innocent - so long as they stay out of his way)
At the end of the day, I think that I'll need to talk at least to the GM regarding my concerns, but I would appreciate opinions on the following before I do:
How much should other players be aware of my plans?
In-game, my PC has managed to avoid divulging most of his backstory to the other PCs. Usually, when this has come up, he's been able to casually provide vague answers and change the topic without too much prying. Bits and pieces of backstory have appeared from time to time - knowledge of strange arcana, familiarity with strange languages, etc. - but the other PCs have mostly let it slide. Out-of-game, players probably have a better idea of what I'm planning, although they may not be aware of how far I'm willing to go to do what I feel like my character would do.
How careful should I be about players' reactions to having my PC manipulate other PCs?
My PC is a fighter - a fairly high-intelligence fighter, FWIW, but a fighter nonetheless, and to accomplish my PC's goals will almost certainly require help - and who better to help than the other PCs? Out of combat, my fighter's intimidation and knowledge checks are solid, but for diplomacy, bluff, spellcraft, casting, etc., there's not much for it. A few points worth mentioning: (a) none of my plans would (at least directly) harm any of the other PCs, and that's certainly not my PC's intention in any event; (b) I would have no problem being made to roll checks to convince the other PCs to help me (bluff, persuade, etc.), and would gladly role play the result upon failing; (c) these activities aren't completely outside what we'd be doing anyway, and doing them would have other advantages for the PCs (i.e., I won't be hogging the show).
If my character does manage to enact his revenge (and he may never finish doing so), assuming the actions are metaphysically evil (e.g., knowingly killing a good-aligned entity, etc.), does this make my character evil? What about the other PCs - are they evil? If not, do they turn on me?
I enjoy playing and don't want to do anything to jeopardize the game; that said, my character has a bit of the Inigo Montoya - you killed my father, prepare to die! thing going on, and the GM basically just told me where to find the guy I've been looking for (not quite, but dropped a huge clue). None of the PCs are of classes that would necessarily suffer from an alignment shift (I think), but how would performing these almost surely evil acts affect how my character is expected to play the game from then on?
