Question: Can I paint a character black and even make readers think he is the antagonist only to find in the second book that he wasn't a bad person after all? Would that be double-standard, because in the first novel, this character even killed people and caused chaos. Would I be disappointing readers?Answer:
You mean a bit like Snape in the Harry Potter series?
He's just one example, of course. Many authors have made effective use of a character whose agenda is not revealed to the reader or the main character until later in the series/story, so that they jump to the wrong conclusions about him at first.
The trick is to make sure that, even when your character seems to do bad things, he is acting in accord with his true agenda so that when his agenda is finally revealed the reader can see that everything he did made sense.
You may also want to plant a few clues in the first book that suggest your character is not entirely what he seems, again so that when the truth comes out the reader can say, "Oh, I should have known."