Karissa @ The Senseless and Sparkly wrote a really interesting post about villains, and I wanted to expound on something she said. I shall quote it below:
"[My character] was sick. One of the sickest characters I've ever written, but he almost convinced me that he was the good guy."
That is the key to writing a believable antagonist. They are the hero in their eyes. Let's go over some examples.
Ronan: Guardians of the Galaxy
Ms. Grunion: Mr. Peabody and Sherman
(Yeah, I liked this movie, shut up)
Ms. Grunion worked for child services. After Sherman bit a girl in a fight at school, she decided that Mr. Peabody, a dog, could not be a suitable parent for Sherman, a boy. Throughout the movie, she tried to remove Sherman from Mr. Peabody's care. I will leave the end unspoiled, but considering this is a children's movie, I'm sure you can guess how it ends.
Jim Moriarty: Sherlock
Moriarty is...*ahem* special. From what I can see, he knows he's evil. He knows he's a criminal, but he revels in it. He's evil and proud of it. Moriarty is a special man and a truly scary villain, but he doesn't try to convince us that he's the good guy. He's the villain we all love to hate.
What do you think about your antagonists? Do they try to paint themselves as the good guy or do they revel in their evilness?