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I understand your question as asking: is it possible for the reader to know that a certain character is evil, from that character's introduction, and before that character actually commits any evil...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/47681 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
I understand your question as asking: is it possible for the reader to know that a certain character is evil, from that character's introduction, and before that character actually commits any evil acts? This precludes having the character commit some crime that is unrelated to the main action, so that we recognise their evil. It also means it is irrelevant to consider things like plot twists and red herrings, because we _want the reader to know_ that the character is evil, we just don't want to make her do anything evil yet. You're also not looking for an answer like "you have to foreshadow it" because the question is _how_ do we foreshadow, or rather clearly signal, that the character is evil. Finally, it's not even about characterisation: you're not asking how to let the reader know the character is nasty, as the trait you want to convey is _evil_. (This last assumption is perhaps the least necessary one; perhaps you don't need to immediately convey the evil of your villain, but can show us she is a vile person with the _capacity_ for evil; but I don't think that's the question, so I won't go into it here.) I'm also assuming you don't simply "tell" us she is evil (e.g. an omniscient narrator saying "people liked her, but actually she had a wicked heart"), or "show" us in a way that is just a trivial shortcut: " 'man, I haven't killed anybody yet, but I'd _love_ to murder a bunch of people if I could get away with it,' she thought". The main solution I can think of involves _tropes_ and _cliches_. Now, this may sound bad, and often we talk about tropes and cliches being used badly; however, sometimes, they are, simply, signalling mechanisms that a storyteller can use in order to signal certain ideas to her audience. A classic example is the "kick a puppy" trope. Now, don't get me wrong, kicking a puppy is a vile thing to do. But if we're talking about e.g. some uber-powerful arch-mage who can wipe out a city with a storm of fire, or some military top-brass guy who can, well, do the same thing--and the story does, in fact, involve the possibility or actuality of crimes on that scale--then kicking a puppy is _not_ on the same scale as the main crimes that will make the character evil. So, we show the character kick a puppy, and (for a modern, western audience at least; I don't necessarily know about other groups) we instantly know this character is a horrifyingly evil monster. "What sort of person would kick a puppy for fun???? And this guy controls nukes???!! Aaaaargh! We're in trouble!" Of course, we can play with any number of tropes or cliches to get the same effect. If you're writing in America you might get the same effect simply by making the character a communist, and if you were writing in the Soviet Union you could simply have made her a capitalist.