Quick Answer: Chuck's reception by viewers has dubbed him a villain the same way Skyler became a villain to Walt, as a family member getting in the way of the actions of the show's central character. Meanwhile, Chuck's medical condition and repressed angry emotions draws parallels to Walter.
Better Call Saul (2015-) is a series without any heroes. Its cast is comprised of people from various rungs on the morality ladder, with nobody sitting at the top. Even for its likable protagonist, we know how things end up. The show's prime focus is examining the way people behave and the way we interpret, punish, and forgive those behaviors. It asks whether technically immoral deeds are forgiven if done for good reasons, and the opposite for seemingly good deeds done for personal gain. This tricky moral positioning of characters opens up a lot of comparison points to the series’ big brother, Breaking Bad (2008-2013), and its subjects.
The Jimmy McGill (Bob Odenkirk) we witness during the first two seasons of Better Call Saul is a man who still possesses a soul. Yes, he used to be a small-time criminal and robber, but his law career was designed with the best intentions of being respectable. He tries very hard to impress his brother Chuck (Michael McKean), co-founder of hugely successful and respected law firm HHM, and he wants to do good work that would boost the reputation of the family name. But as the various realities of Jimmy's life chip away at his best intentions, we see him starting down the path that eventually turns him into Saul Goodman, the criminal lawyer we first met on Breaking Bad. Jimmy just isn't there yet. He hasn't crossed the line from which there is no turning back. He’s still the one we root for. He’s the star of the show -- and as the star of a show, he needs a villain. For all intents and purposes, Chuck is that villain. In being that villain, he embodies many of the characteristics of Breaking Bad's villain-apparent as assigned by the eyes of the audience, and of its star, who transitioned from protagonist to villain during the show's five seasons.
Bob Odenkirk and Michael McKean
Breaking Bad’s family matriarch Skyler White (Anna Gunn) was a hotly contested character on the series. Anna Gunn even wrote a New York Times piece about the passionate hatred dished towards her character across the internet, calling Skyler everything from a “shrieking, hypocritical harpy” to an “annoying bitch wife.” People weren’t keen to consider the emotional and psychological torture a person in her situation would have had to endure. People weren’t open to considering her perspective as someone forced into a life of murder, drugs, and criminality as the spouse of one of the biggest drug dealers in the western United States. She was seen as someone at odds with the show’s main character, a man we were taught to initially love and sympathize with as he suffered from terminal cancer and cooked meth to financially benefit his family - to benefit her - which was an act we could understand as people living in a country wrecked by unfathomable medical expenses. It didn’t matter that Walt eventually morphed into something completely different, a person completely on par with the Gus Frings and the Tuco Salamancas of his world. Walter is the star. He’s the man, and Skyler sucks. She became a villain working to stop the guy we were supposed to be cheering for.
Jimmy McGill is a similar entity. He’s witty, charming, intelligent, and tries really hard to succeed as a legit lawyer to no avail. So what else is he supposed to do? We know he becomes Saul Goodman, who beneath his charm and humorous demeanor is a pretty crappy guy, yet we liked him on Breaking Bad -- and now, we like Jimmy even more. Why? Because we like Chuck less. Just as we always had someone to like less on Breaking Bad, we have someone to like less on Better Call Saul.
Chuck is this show's Skyler “getting in the way” of Jimmy’s work. He is the family member who can’t understand things from Jimmy’s perspective, who responds to every idea with disdain, and who emasculates our amicable hero every chance he gets. What makes him even more of a Skyler is that, in most cases, he is right. And even beyond that is the way audiences have responded to him. While Chuck's medical condition garners some level of sympathy for his actions and behavior, he is still widely disliked as a square and a brute and a loveless jerk getting in the way of the devilishly fun antics of our lead character. The lack of Chuck’s existence in Breaking Bad makes us wonder what happens to him along the way and fuels a desire to witness his all but inevitable removal from Jimmy’s life. Knowing that Jimmy thrives in Breaking Bad and Chuck is nowhere to be seen makes Chuck feel more like a loser, more like an obstacle that needs to be overcome, than the less-crappy we’re supposed to be cheering for.
Bob Odenkirk and Michael McKean
Chuck’s medical condition plays a big part in his characterization. It is so rare and unbelievable that it’s almost impossible to take seriously, coloring everything he does as we’re not entirely convinced his struggle is real. His condition is a metaphor akin to Walter’s cancer, which served as the catalyst for all Walt's eventual cancerous malice that spread across New Mexico and took many more lives than his own. Chuck isn’t just a guy who acts like a jerk because he’s suffering -- he is a jerk who gets away with being a jerk because of his eccentric condition. He may be incessantly concerned with following the rules and doing things by the book, but that doesn’t make him a good guy, or stop him from being a domineering brute to his brother for little more than a than childish superiority he can't forget.
There exists heaps of jealousy between Chuck and Jimmy stemming back to their younger years. Chuck was a star student, successful early in life and who established a sterling reputation after finishing law school at age 23. Meanwhile, Jimmy’s misfit antics started as a teenager when he stole money from the family business, ruining their father's life's work. Yet Chuck felt Jimmy was more loved by their parents all the way through the moment of their mother's death, and he has never let it go. Chuck may play by the rules and seem like the bigger man, but he is no better a person than Jimmy. If anything, Jimmy is a man with tremendous concern and compassion for his brother despite receiving nothing but belligerence in return. Jimmy is not yet detached from the consequences of his actions. He has sacrificed his own interests on numerous occasions to ensure Chuck is okay, only to be repeatedly gunned down as thanks. Chuck embodies Walter White’s sense of fiendish superiority by habitually taking advantage of Jimmy’s love. As Bob Odenkirk said to EW, Jimmy "never meant to put his brother’s life in danger. But I think he underestimated how important it was to Chuck that Chuck be right. I think he underestimated how important it was to Chuck to just be the smartest guy in the room. It’s practically life and death for Chuck that he be the smartest guy in the room, and that no one take that away from him, ever, not even an ounce of it."
Chuck plays on Jimmy’s love in the second season finale, “Klik,” when he sets up the foil-covered room in order to look like he’s finally tipped over the edge of sanity, hoping to use his medical condition to get a confession from his brother. "It was me. I woulda made Nixon proud," Jimmy says. "It all went down exactly like you said, I mean exactly. I doctored the copies, paid the kid at the shop to lie for me, it is insane how you got every detail exactly right. So you can relax, okay, because that brain of yours is chugging along at 1000 percent efficiency." Jimmy only confessed because he wanted to make Chuck feel better. Chuck only captured the recording because he needs to be right. What does this say? Chuck has a very similar personality to Walter White -- one guided by narcissism and bitterness based on years of bottled-up resentment. It makes sense that the future Saul Goodman is so patient and attracted to the repressed and sick version of Walter White who first steps into his law office. The person sitting before him struck a chord that reminded him of his brother. And like Chuck, Walt would grow to not appreciate or respect Saul nearly as much as he should, and both times Jimmy would remain loyal far longer than his best interests would dictate.
Vince Gilligan and Peter Gould's central characters on these series all run the gamut of likability and detestable behavior. Better Call Saul's players are rich and complicated and each has the ability to test our allegiances as viewers and present us with compelling situations that challenge our perceptions of what is good and bad, right and wrong. Chuck may be receiving a Skyler-esque hatred for his tendency to challenge and thwart the series protagonist, but he earns it by operating as a self-absorbed jerk who is preoccupied with his own interests.