What makes people like unlikeable characters?

[Nondescription]

I think it boils down to good writing. Using your Zuko and Mako example: I believe that Zuko was a better jerkish character than Mako because he had a extremely basic motivation (wanting to earn forgiveness for past mistakes/fearing that he would never be 'good enough' ever again) that was clearly defined. Despite the fact that Zuko was a jerk, people can empathize with making such an awful mistake that they screw themselves over, and that feeling of wanting people to just give them another chance. And what did Mako have? A clear motivation, but it was too complicated (my parents died at the hands of a firebending mugger, so I'm looking for someone to fill the void/I will fiercely protect everyone I love). Had they simplified Mako's motivation to something like "I feel like I am never strong enough" or "I hate being abandoned/abandoning someone" that is far more relatable, because most people haven't had their parents immolated by petty thieves but nearly everyone has felt inadequate at some point in their lives.

And then of course these characters have to use their motivations to change themselves for better (usually heroes) or worse (usually villains). Zuko changed, no doubt about that. Did Mako? I dunno, I couldn't tell if he did or not. But to be fair, it's kind of hard to draw motivation solely from the death of your parents and nothing more.

[justadarling]

I think how well the audience can sympathize with and relate to the character plays a key role.

People like Zuko because they can relate to him and feel where he comes from. He's not just some evil person hunting Aang so the Fire Nation could take over the world. He's hunting Aang because he wants to regain what he lost (his honor) and earn what he never felt he had (his father's love). How many teenagers want to feel loved by their parents? How many kids feel like their parents play favorites or that they fall in the shadow of their siblings?

Another reason why people adore him is because the writers did a great job of making the audience root for him. You feel sad and attached to him because you see him struggle. He wants to do the right thing but he struggles and falls back in his old ways and hates himself for it. You see that inner turmoil and you want him to do the right thing because he's trying so hard. You feel good when he makes the right decision (like freeing Appa from Lake Laogai) and you pull your own hair every time he stumbles (like in the Crossroads of Destiny). You want him to succeed.

His past pulls on your heart strings. How did you feel when he begs his father not to make him fight and he gets his face burned? Or when Iroh teaches him how to redirect lightning and he's yelling out for the world to strike him because he could take it and give it back, only to have nothing happen and fall to his knees, crying? You feel his pain. I absolutely cannot watch the Zuko Alone episode when he helps this family only to have them hate him once they find out who he is. Not to mention they keep you interested with the whole "Where. Is. My. Mother?" business.

And at the end, rooting for him the entire time was rewarding. You get to see him succeed after the whole two steps forward- one step back path to being a "good guy". You get to see him overcome his demons. Everyone can relate to what he learns. He thought his destiny was handed to him by his father, represented by the scar on his face. To our delight, he says ******** you to dad and with the help of his most important father figure, takes destiny into his own hands. Who doesn't want to be the master of their own destiny?

Mako is disliked because he has the jerkiness of Zuko and not even half the development. Poor Mako lost his parents and had to sacrifice his childhood for Bolin. That's hard. But you don't see it basically become his identity the way that Zuko's hardships and people don't sympathize as much. Also Zuko never "plays" girls the way that fans think Mako does, which is where a lot of the fans have problems with Mako.

tl;dr The audience could relate to Zuko's hardships and sympathize with him. They understood why he was a jerk and overlooked some of his more nasty points because of the obvious effort he put into changing himself. Zuko's character allowed for people to realize he was flawed but root for him at the same time. We like characters who we can feel for, relate to, or admire, despite their obvious flaws. Dr. House is a huge a-hole but he's funny, brilliant, and saves lives. You need to have qualities redeeming enough to make the audience feel like it's worth overlooking the not so great qualities