But as the show has gathered both critical and commercial steam, Aaron Paul's turn as Walt's former student and business partner Jesse Pinkman has become every bit as crucial to its success.
Conceived initially as a druggie slacker who would show Walt the ropes of the meth underworld before being unceremoniously offed, Jesse has evolved into the beating heart of Breaking Bad, offering an essential contrast to the increasingly morally compromised Walt.
The role won Paul a thoroughly deserved Emmy for Best Supporting Actor following the show's third season, and he is nominated again for its fourth.
With the fourth season now finally available to UK viewers via Netflix (and on DVD as of October 1), Digital Spy caught up with Paul to talk about Jesse's progression, his favourite episode from the show's run, and the advice he took from co-star Bryan Cranston.
Note: This interview contains spoilers for the fourth season of Breaking Bad.
Jesse wasn't originally intended to be such a major role – what was your first impression of the character, and how did that evolve?
"When I first read Breaking Bad I thought it was brilliant, but there weren't too many layers to Jesse at the beginning. I initially viewed him, as did everybody else I think, as just a burnout druggie. But then even as season one went on, and especially when season two started, he had so much more going on beneath the surface. You really saw that he was a good kid, he had a good heart, but he was definitely lost and struggling to find his way."
The chemistry between you and Bryan Cranston is so strong, and so central to the show - how do you approach your scenes together?
"It's been like that since day one. The first scene we did together, we just really hit it off, just gelled. Each scene's different – he and I will run lines outside of our trailers. It's a very light set, because we tell such a dark story at times, and we've gotta break that darkness up with some light and humour. It's such a fun set, and a family that I will miss dearly when it's all over."
Talking specifically about season four, what can viewers expect from Jesse's arc following that very dark ending for him in the third season finale?
"I think the fans know by now that each season proves to be the darkest one yet. The rollercoaster ride just keeps getting crazier and crazier, and season four is hands down the most intense one we've ever had. Jesse's in a very dark place – he didn't want to kill Gale, but he felt backed into a corner.
"Before Walt saved his life, he was willing to be a martyr and just go out guns blazing when he went after those drug dealers. He knew he was probably going to end up dying and he didn't care, he just needed to get rid of them. But Walt saved his life, and so he felt like he owed it to Walt. So in season four, he has to figure out how to live with those demons."
You have a lot of those very heavy, emotionally intense scenes to play – how easy do you find it to leave that behind when you finish for the day?
"It really depends. Some days are harder than others, you know, you go home after crying all day on set, and I try to stay in character as much as I can, it just helps me with my whole process. But you know, you gotta shake it off, I think it's unhealthy if you just keep inside of that skin.
"What every single one of these characters is going through is so intense, and the first couple of seasons I would really try to be in character constantly. I would goof around on set, but I would generally just be so intense, and Bryan said to me 'You know, it's okay to just shake it off, it's okay to take a break from it'. And he was absolutely right. But he's a much better actor than I am – he's more of a professional than I am!"
Jesse and Walt's relationship is endlessly intriguing – why is Jesse so loyal to Walt, even when he treats him so poorly? Is it that desire for a father figure?
"You said it, I think. Jesse is in search of that. He wants to be told what to do, he wants to have some sort of person to look up to. He needs that in his life, because his parents completely gave up on him, he doesn't really have anything in his life. He has no stability, and Walter White – Mr White, as he calls him – is definitely his father figure, his stability. He desperately wants that guidance from him."
There's some divided opinion among fans about whether Jesse should find out about Walt's actions with Jane and Brock – where do you come down on that?
"Yeah, ugh, I don't know. I personally would want him to find out, I think, but then if I'm thinking about Jesse... do I want Jesse to go through those emotions? Because it's jabbing the dagger even deeper into his side and twisting it. So maybe it's best that he doesn't know. What would be the point of telling him? It would just make him even more sad, I think. I'm a bit torn on that."
Vince [Gilligan, the show's creator] has talked a lot about the moment where viewers finally lose all sympathy for Walt – what was that moment for you, or are you not there yet?
"No, I'm definitely there! I am absolutely there! You know, there are so many moments. It started, for me, when he allowed Jane to die. I know Jane was a bad influence on Jesse, but Walt could have gone about it in a different way. He did not need to allow that to happen. But the poisoning of Brock was pretty unforgivable.
"The thing is, Jesse was right all along when he showed up at Walt's house, so distraught and [with a] gun pointed to his face. He was right! And so if Jesse were to find out that Walt was behind any of that, we know what Jesse would do."
If you had to pick a scene or episode that defines the character of Jesse, one that's particularly special to you, which would that be?
"I think probably when I read 'Peekaboo', in the second season. It's an episode that really focuses on Jesse's storyline, where he tries desperately to save this little boy from his cracked-out parents. And it just really showed me, and our audience, what Jesse was all about, and how he did care. So many more layers were revealed in that episode, and it definitely guided me in the direction where Jesse is now."
What ending would you like to see for Jesse?
"I would love Jesse to just break away. Go to New Zealand and become a bush pilot. Seriously, that would be great! Have him just never look back, and start a new life. But with Breaking Bad you can't count on happy endings, I don't think. I just hope Jesse survives."
The fourth season of Breaking Bad is available now on Netflix.