Nikanor, or Nicanor, is a historical figure we know almost exclusively from 1 Maccabees and 2 Maccabees. He was a Seleucid general who served in Judea during the Maccabean revolt, and who had to be defeated by the Maccabees to break the oppressive yoke of the Hellenistic Kingdom of Syria. In a sense, he's the major antagonist of the whole story.
Famously, though, 1 Maccabees and 2 Maccabees give very different impressions of Nicanor. 1 Maccabees takes an unrelentingly hostile view of him:
Then the king sent Nicanor, one of his most distinguished officers and a bitter enemy of Israel, with orders to destroy the people. Having arrived in Jerusalem with a large force, he sent to Judas and his brothers this deceitful message couched in peaceful terms: “Let there be no fighting between you and me. I shall come with a small escort to have a peaceful meeting with you.” When he came to Judas, they greeted each other peaceably, but the enemy had made plans to kidnap Judas. When Judas became aware that Nicanor’s visit had a treacherous purpose, he became afraid and refused to meet him again. (1 Macc. 7:26-30)
Thus Nicanor is recognized (1) as an enemy of Israel (2) who has orders to destroy the people and (3) who sends a lying offer of peace (4) in which his plan is really to kidnap Judas; (5) Judas becomes aware of this and avoids him.
2 Maccabees gives us a very different picture:
The king immediately chose Nicanor, who had been in command of the elephants, and appointed him as governor of Judea. Then, he sent him forth with orders to put Judas to death, to disperse his followers, and to install Alcimus as high priest of the great temple. However, when Nicanor heard of the bravery exhibited by Judas and his men and how courageously they always fought for their country, he became reluctant to allow the issue to be settled by bloodshed. Therefore, he sent Posidonius, Theodotus, and Mattathias to negotiate a treaty of peace. After a lengthy discussion of the terms, each leader explained them to his troops, and all were of one mind in favor of accepting them. On the day decided upon for the respective leaders to meet privately, a chariot came forward from each side, and thrones were set in place. Judas had posted armed men at strategic points to prevent any sudden act of treachery on the part of the enemy. In this way, the conference was held without any complications. Nicanor stayed on in Jerusalem and did nothing there that could be construed as a hostile act. He sent away the crowds that had rallied to him, but he always kept Judas close to him, for he became deeply attached to him. He urged him to marry and have children, and Judas did marry and settle down to lead the quiet life of an ordinary citizen. (2 Macc. 14:12, 18-25)
Thus Nicanor is (1) reluctant to harm the people, (2) despite the fact that he has orders to do so, and to do that (3) genuinely tries to negotiate a treaty of peace and (4) becomes deeply attached to Judah Maccabee (5) who becomes friends with him.
Very different pictures. There is no actual contradiction. The author of 2 Maccabees is clear elsewhere that the book is an abridged adaptation of another work, and that the author is deliberately taking complicated events and trying to tell an uncomplicated story with them. Thus 2 Maccabees is explicitly not giving a direct history, but an easy adaptation of a way those events have been seen. It is also more removed from events in another way; it was written, probably Hellenistic Egypt, in Greek, and is giving a depiction of events from this sort of external perspective. On the other side, 1 Maccabees covers a more extended historical period, with the inevitable result that it only focuses on what is essential to the story it is telling, and is very clearly a Hasmonean Kingdom account of what the Hasmonean dynasty was about. 1 Maccabees has a consistent theme of judgment of oppressors, and so tends to emphasize things that bring that out. 2 Maccabees, on the other hand, has a consistent theme of God's mercy to Israel on behalf of the Jewish martyrs, and so it tends to emphasize things that bring that theme out. They are both unabashedly from a particular point of view, and there is no more contradiction between them than there is between two different points of view on the same events.
What really strikes me though, is that even if one took them straightforwardly, there is no actual contradiction, either. All of the following can be true together:
Nicanor was opposed to Israel and had orders to destroy them.
He was actually impressed by the people of Israel and wanted to avoid unnecessary bloodshed.
He opened negotiations with a double purpose to bring peace with minimal bloodshed and get Judah (the major obstacle to it) out of the way.
He ends up actually liking Judah.
He tries to encourage Judah to stop what he is doing and settle down.
Judah becomes friends with him, and begins to follow his advice.
Judah at some point becomes aware of Nicanor's original deceptive intent and begins to distance himself from him.
And when we look at how this all ends, of course, we find that both 1 Maccabees and 2 Maccabees agree that this did not end well for Nicanor, and that the Jews in the end had Nicanor's head cut off and displayed. (2 Maccabees is even very clear that this was authorized by Judah.) This is entirely consistent with everything above. 2 Maccebees claims that Alcimus -- the guy the king had appointed high priest -- forced Nicanor's hand by accusing him of treasonous intentions due to his friendship with Judah, leading Nicanor reluctantly to break his agreements with Judah. Thus the 2 Maccabees version of Nicanor ends in exactly the same place as the 1 Maccabees version.
I think one can argue that this is partly the point, and is the point with less obvious cases in, e.g., the histories of the kings of Israel and Judah in the Old Testament. People are just this complex, and understanding them historically requires taking into account both the fact that people can have different legitimate perspectives on them, due to having different purposes in view, and the fact that they themselves can have layers of motivation in their choices and decisions. This is one of the lessons we have to learn in order to deal with people. It is also one of the most difficult things to learn.