How to make your players hate your villain

[Brother Fen]

I like the dreams/nightmares suggestion. In order to make the characters hate him, they have to be emotionally invested. I'd suggest making a NPC that helps the party such as a guide or some friendly local. Make the NPC susceptible to the dreams/nightmares and become visibly upset by it. By the end of the session, the NPC succumbs to the nightmares and slashes his own throat in front of the characters. This gives them a reason to hate the villain and want revenge for their poor friend.

[The Mortonator]

I am doing something similar in a game I will be starting soon. My approach thus far hasn't really tried to get the PCs to hate this guy, they have no idea who he is, but to get them invested when he returns.

Basically, this guy is Deathwing. If he comes back, then it's a world changing event. They aren't really supposed to know who he is, so that if they do unleash him it's a surprise. But his effects will be instantly felt around the entire world. The landscape entirely changed in his image and the core rules of the world altered.

[Sissyl]

For the imprisoned evil threatening to return, I have never seen a better emotional impact than in Akira.

Spoiler:

He is the biggest, most dangerous mystery around. Nobody knows when or if he will return. The people set to deal with it have unlimited budgets. The further the action goes, the more inevitable it all becomes. More and more, suggestions, themes recur. And then, of course, he returns, triggering another great cataclysm. And only then do you really understand why.

[Helcack]

You could just have him be like the guy who scarred an entire generation of people so that they are so afraid of something associated with him that they scream and try to kill it on sight(better if it's something people tend to like such as dogs or birds).

[Brother Fen]

I used a bit of my own advice in a scenario two weeks ago, when I added an extra NPC with the intention to kill them early in the session so the PCs would take the villain as a serious threat. It worked well, but perhaps a bit too well, as the players really liked the NPC and were bummed about seeing her die.

[Crimeo]

Maybe give him spell mastery with only a list of certain spells you want him to be able to use for hatred purposes as his mastered spells?

This way, you can make it so that he is in a magical tower somewhere with his spellbook taken away, but is still able to act in certain limited capacities, perhaps without jailers knowing. But not EVERY way / may not be able to escape, only meddle.

For example, one of his few mastered spells might be "Dream", allowing him to still taunt PCs, communicate with minions outside, etc., yet not escape.

Other potentially nice choices could be "Discern Location" making PCs hate him and want to kill him because he can continuously pinpoint them and relay the info to other bad guys, even from prison. (only if you're okay with your BBEG being level 15!).

[edit, just realized this was an update on an older question, oh well.]

[Lamontius]

build love first
or sympathy
then wrench it away and do something savage

then they will hate it

[The Sword]

In the Wheel of Time (Eye of the World) the most evil character is a pedlar who betrays them. The combination of casual cruelty, singlemind determination and 'watch the world burn' mentality is very evil.