In Battlestar Galactica (2003), any serious conflict between the Cylons amounts to this, since all but the five originators of the race are brothers and sisters by relation.
John murdered his brother Daniel out of jealously because his mother loved him more, polluting the models during their assembly process. He later kills half his siblings for rebelling against him.
Boomer and Athena's interaction also becomes increasingly hostile as Boomer feels that Athena got the life she should have had. Athena knowingly started out as a Cylon before joining the humans willingly, while Boomer believed herself to be human before having her Cylon nature forced upon her. She threatens to kill Athena's daughter Hera before Six kills her. After downloading again Boomer later beats up Athena and ties her up, then forces her to watch as she makes out with Athena's human husband Helo and kidnaps her daughter for Cavil.
In Batwoman, it becomes clear early on that the villain Alice is actually Kate's long-lost fraternal twin sister Beth. Kate tries to stop Alice, while simultaneously doing her best to reach Beth inside the murderous criminal. Alice also quickly realizes that Kate is Batwoman and not only keeps her secret but also saves her once from another criminal.
In Beetleborgs, at the start of the Metallix season, the kids contact Arthur "Art" Fortune, the Stan Lee-like creator of the comic book, to revamp their superhero alter-egos. Meanwhile, the villains hook up with Lester "Les" Fortune, his jealous and psychotic brother who is serving a prison sentence, to draw new minions for them. Working for opposite sides only propels the brothers' long-time hatred for each other.
Cesare and Juan of Borgia — an unrelated show based on the same piece of history — also use this trope. Subverted, because it's revealed that Cesare didn't kill Juan. And then double subverted, because Juan's other sibling — his unsuspected, seemingly innocent little sister Lucrezia — did.
Tommy and Michael Caffee in Brotherhood. Tommy is a up-and-coming state politician with a young family; Michael is a senior figure in The Irish Mob with a Hair-Trigger Temper. As the series progresses, it turns out they're Not So Different morality-wise, but they remain at odds with each other.
Buffy the Vampire Slayer: Caleb, The Dragon to the final Big Bad, identifies Faith as 'the Cain to Buffy's Abel' in his first appearance. Faith later concedes that jealousy over not being the Chosen One probably contributes to her tendency to be at Buffy's throat and to her going rogue in earlier seasons.
An episode of Cheers ("Ma Always Liked You Best") involved Woody bonding with Cliff's mother and Cliff becoming jealous, leading Mrs. Clavin to say she wanted to avoid "a Cain and Abel situation" and agreeing that they may "share" her.
Horatio and Raymond Caine in CSI: Miami. Horatio and Ray are portrayed in direct contrast to one another, with Horatio portrayed as a Good Cop to Raymond's Dirty Cop. Some episodes in the earlier seasons of the show had Horatio dealing with indiscretions Ray (who was believed to have been murdered while undercover but was actually Faking the Dead the whole time) had committed while undercover, including fathering a child with another woman, getting involved with criminal gangs and drug addiction. It was also implied that Horatio had feelings for Ray's wife Yelina, a Story Arc that never got resolved after Ray came out of hiding to reunite with Yelina and their son (but later got Killed Off for Real anyway, dying in Horatio's arms).
J.R. and Bobby Ewing from Dallas are a perfect example, with J.R. as Cain and Bobby as Abel. Though Bobby was the one that once tried to drown J.R. in Southfork's swimming pool.
Dark Desire: Estaben and Leonardo are brothers, who initially are close. However later they get in a physical fight when Leonardo has wrongly thought Esteban is having sex with his wife, threatening him with a gun over it.
In Deadwood, Francis Wolcott is buying up all the goldmines around town for Hearst. In the case of one mine owned by two feuding brothers, he manipulates one brother to murder the other in order to get the sale.
Dexter Season 1 focused on Dexter and Brian/The Ice Truck Killer, who was Dexter's biological brother. He served partly as an example of what Dexter would be without the Code of Harry and cleared up heaps of backstory. In a twist on the usual story Dexter killed Brian. I'm not sure which one was Cain and which was Abel
Subverted: even when siblings and death occur, it's not about sibling rivalry per se.
The Doctor and the Master. It's never been confirmed on the show that the two are actual brothers, and the Doctor denies this in the revived series although the Doctor isn't the most reliable source when it comes to his past. Even if they're not biologically related, the series makes it clear that they were as close as brothers growing up, so it still counts.
In the extended universe there is a character who is actually heavily implied to be the Doctor's older brother, namely Magnificent Bastard Irving Braxiatel. It is revealed that in an alternate timeline, the Doctor actually murdered him!
A less extreme version occurs in "Carnival of Monsters". President Zarb's policies, such as allowing aliens onto Inter Minor, are opposed by his brother Kalik, who tries to release the dangerous Drashigs into the city to force his brother to resign. Ironically he ends up getting eaten by the Drashigs.
"The Unicorn and the Wasp": The last murder victim is Roger Curbishley, killed by his older, illegitimate, half-alien brother. However, Roger had no idea that he had any siblings, and it's not known whether or not his brother killed him out of jealousy, homophobia, or because Roger saw him change form.
The Flash: in Season 6, this seems to be the relationship between Iris's assistant Allegra and her cousin Esperanza. Both can project UV rays from their hands, but Esperanza is perfectly willing to kill, while Allegra desperately wants to be good.
A French Village: Daniel and Marcel are very much opposites. Daniel is bourgeois: a doctor, deputy mayor (then the mayor when his superior dies) and moderate politically. Marcel is a manual laborer, Communist activist and committed to the revolution. The pair are also very different in temperament. Daniel is far more calm, temperate and very tolerant about others' actions. Marcel is hot-headed, quite reckless and holds deep grudges.
Stannis Baratheon is the Cain to Renly Baratheon's Abel. However, Renly was the younger brother who intended to usurp the throne, despite Stannis offering to make Renly his heir, and if Stannis hadn't killed Renly, Renly probably would have killed him, as he tells Catelyn that he plans to destroy Stannis' army in the morning with no mention or hint of sparing Stannis, though Stannis shows remorse over Renly's death. Furthermore, Stannis is the underdog with the much smaller army. However, Stannis himself cites it as a precedent when Davos tries to defend Gendry by invoking that blood is Thicker Than Water.
Gregor (Cain) and Sandor (Abel) Clegane despise each other intensely, ever since Gregor melted Sandor's face in a brazier, though this is only the tip of the iceberg for them, and would rather fight each other than team up. However, except for a brief spar in "The Wolf and the Lion" where Sandor "defended" Ser Loras, and the two of them appeared quite willing to fight to the death in full view of the court for very little reason, they have never come to blows. Until the penultimate episode of the series, when Sandor confronts Gregor in the middle of Daenerys laying waste to King's Landing; Gregor immediately abandons his duty to Cersei to engage his brother in a brutal fight that ends with Sandor tackling him out a window to their mutual death. DVD extras reveal that this relationship is actually the basis for why Sandor worked for the Lannisters more directly; he was unwilling to live under the Clegane roof once Gregor became head of the house.
Selyse Baratheon née Florent is an enthusiastic participant in her brother Axell's human sacrifice for nonconformity in the Season 4 episode "The Lion and the Rose".
Ramsey Bolton feeds his dogs with his baby half-brother. He wasn't this with Domeric, who died of an illness.
Euron Greyjoy murders his brother Balon so he can take his place as king. And if Balon is the Abel of this relationship, that really speaks volumes about Euron.
General Hospital: AJ (Cain) and Jason (Abel) Quartermaine. AJ was the alcoholic perpetual screw-up who spent the first few years of his life being shunned by his father because he mistakenly thought he was the result of his mother's adulterous affair—it's entirely likely that this is the very reason AJ was so messed up. Jason was the "golden boy" to the point of being a Purity Sue—straight-A student, varsity athelete, steady girlfriend, plans to become a doctor like both of his parents (ironically, he was the result of his father's adulterous liaison, yet was never shunned by his adoptive mother as his father shunned AJ). Things came to a head with Jason jumping into a car to stop a drunken AJ from driving and AJ crashing the car and therefore killing Jason just as Cain killed Abel, albeit unintentionally (Jason recovered physically but never regained the memory of his old life, becoming an entirely new person). Despite the malevolent turn in Jason's personality, his loved ones still saw him as the old Jason and continued to treat AJ as the lesser brother.
Subverted by the Valeska brothers in Gotham. Jerome initially appears to be the Cain when he scars Jeremiahs face with acid. But Jeremiah turns out to be no better.
Sean and Eric Renard of Grimm. At this point, it looks like Eric is Cain to his half-brother's Abel, but it can be hard to say with these two. Their problems include serious philosophical differences about how the Wesen world should work, probable rivalry for power (Eric would seem to have the edge, being the legitimate royal, while Sean is the product of an extra-marital affair on their father's part), and the question of which one is the father of Adalind's child. Granted, neither knows about this last problem yet, but it's just waiting to be used against both of them.
In an interesting variation, Nathan and Peter Petrelli from Heroes spend the entire first season being set up as this — with Nathan, the older one, being loyal to their crazy Utopia Justifies the Means mother and a bit of a jerk to boot, and Peter, the younger one, representing all that is good and pure and idealistic — but the climax of the first season finale has Nathan ultimately rejecting his mother's side and dramatically sacrificing himself to help Peter save the world. Even if he didn't actually die. Of course, many of the fans believed something like that would happen all along, and were made very happy by the mutual declarations of love that came with it
After the events of Volume 3's finale, it looks like Peter and Nathan are heading into this direction after all.
This was sometimes the case in I Dream of Jeannie. Jeannie's sister (also named Jeannie, also played by Barbera Eden, but with a brunette wig) was clearly evil and often tried to steal Tony for herself, but whether the two sisters were enemies depended on the situation. (Sometimes Jeannie was naive enough to trust her, but not always.)
Kamen Rider Gaim ends up going through this with Mitsuzane "Micchy" Kureshima (the protagonist's best friend) and his older brother Takatora (who is initially made out to be the Big Bad). They actually have a good, but somewhat distant relationship at the start of the series, but as the story progresses, Micchy begins a love-inspired downwards slide while Takatora is revealed to be an idealist forced to be a realist in the face of an alien invasion. Later in the series when Takatora finds out about Micchy, he insists upon being the one to deal with his brother, but is seemingly killed in their battle. He turns up alive, and the show ends with the brothers mending fences and working to repair the damage done to the city by Helheim.
Kamen Rider Zi-O has one of these that drives the entire plot: The Big Bad Swartz is part of a royal family with Time Master powers, but their parents decided that his younger sister Alpina would be the next one to lead the family. In a jealous rage he wiped her memories and dumped her in an alternate timeline, where she was found by La Résistance and given the name "Tsukuyomi". Eventually Swartz finds out that she survived and plots to steal her powers to become even stronger. By the end of the series, the heroes' plan for defeating Swartz involves making Tsukuyomi a Kamen Rider so she can fight him on equal footing (since he's stolen the powers of Kamen Rider Decade). Once or twice Swartz tries to pass himself off as a Well-Intentioned Extremist, but the fact that his sister's mere existence is a Berserk Button for him proves him to be a liar.
Kirby Buckets: To say that Kirby and his sister Dawn do not get along well is really putting it mildly.
KITT and KARR from Knight Rider could arguably be considered an A.I. version of this, with older prototype KARR the Cain to KITT's Abel.
Kyōryū Sentai Zyuranger has Burai's opposition to his brother Geki as much of the focus of the story—eventually however, the two are reconciled and Burai becomes the original Sixth Ranger.
In The Librarians, this is the relationship between Santa Claus and the Patron Saint of Thieves. The latter has always been jealous of his jolly brother and dreams of stealing his sleigh to increase his power. Santa manages to trick him by gifting him the sleigh, knowing full well that the Patron Saint of Thieves is unable to accept anything given freely.
In Lost, it has been revealed that Jacob and the Man in Black are brothers.
Lucifer (2016): Lieutenant Pierce turns out to be the original Cain, still cursed to walk the Earth after the murder of his brother Abel. He insists that Abel was every bit as bad as he was, and that the only difference between them is that Cain won their final fight. Considering that Abel ended up being the very first human soul in Hell, it's clear that Cain has a point. When Lucifer and Cain resurrect Abel in an attempt to remove the Mark of Cain, Abel turns out to be the Biblical equivalent of a rich frat bro, constantly going to parties and trying to seduce women by telling them about his massive flock of sheep.
Bud and Kelly Bundy on Married... with Children are a very strange case. Very often, they are like this, willing to turn on each other and double cross each other, even breaking out into actual fist-fights at times. On the other hand, there have been times when the two have stuck up for one another, and one has defended the other sibling from another tormenor. Kelly has even gone out of her way to dole out punishments on girls who play cruel tricks on Bud. It's likely a case where it is Depending on the Writer, but it's a Big, Screwed-Up Family in every sense of the term.
Arthur and Morgana on Merlin. Arthur is the Abel (the Big Good) to Morgana's Cain (the Big Bad). Morgana spends most of her time plotting to bring Arthur down and has made many attempts to kill him and make him suffer. And it seems as though she doesn't even care even after learning that he's her half-brother. It's a far fall from when she actively defended him in 1x07.
In the Monk episode "Mr. Monk's Other Brother," Monk ends up taking in his half-brother, prison escapee Jack Monk, Jr. When Adrian is in session with Dr. Bell and explains his conflicts he's dealing with (he knows Jack is a fugitive, but at the same time, there are moments that he isn't unbearable to live with), Dr. Bell makes note of the Cain and Abel analogy to explain Adrian's feelings.
One episode of MythQuest retells the story of Osiris and his brother Set. Set is jealous of Osiris' fame, wealth, and power, so he devises a plan to poison Osiris and take his place. When Alex, an Intrepid Fictioneer who is taking the place of Osiris, learns of this, he calls Set "the worst brother since Cain."
The O.C.: Trey and Ryan Atwood, with Trey as Cain and Ryan as Abel. While the Atwood brothers' relationship, which had been tense since the beginning of the series, appeared to be improving when they reunite upon Trey's release from prison, the tension gets pushed to breaking point after Ryan discovers that Trey tried to rape Marissa. The end result is Ryan delivering a No-Holds-Barred Beatdown to Trey, before Trey gets the upper hand, and is prevented from fulfilling the Biblical version of the trope and strangling Ryan to death by Marissa shooting him in the back.
In Once Upon a Time, Regina, the Evil Queen, who's actually in the process of reforming at this point, finds out she has a sister, Zelena, who was abandoned in Oz by their mother Cora, and eventually became the Wicked Witch of the West. Zelena hates Regina because Regina had a privileged life (though even Regina points out that Cora was a bad mother) while she grew up poor and hated in Oz, and was then chosen by Rumplestiltskin as his apprentice despite not being Cora's firstborn or having the same talent for magic as Zelena. Zelena is the Big Bad of Season 3, and Regina teams up with Emma to stop her and save Storybrooke. Eventually, though, Zelena herself turns good, and the series ends with the sisters on good terms.
Dan and Keith from One Tree Hill always had a rivalry because of Keith's love from Dan's ex, Karen. In Season 3, Dan kills Keith because he believed Keith tried to kill him in the previous season; actually it was his then-wife, Deb. Abby who witnessed the murder left taunting messages to Dan which quoted the Cain and Abel story.
The Outer Limits (1995): The Season 1 episode "Blood Brothers" featured two brothers running their late father's pharmaceutical company to discover cures against various fatal diseases, with Spencer (a scientist working in a hazardous chem lab) as Abel and his big brother Michael (one of the company's directors) as Cain. Spencer wants to develop the cure for the general good of mankind, while Michael wants to limit it to the wealthy few to make more profit. Michael eventually attempts to murder Spencer and Spencer's girlfriend so he'll be the only one who knows the secret of the drug. Michael then takes the drug to cure his own Huntington's and his body soon starts to decay due to the side effects, with Spencer unable to cure him.
It comes up again in Power Rangers Operation Overdrive, this time between villains. The season has multiple Big Bads competing with each other as well as the Rangers, and the two most prominent are brothers Moltor and Flurious.
And years before these two series were aired, we saw a bit of this with Ryan (Cain) and Dana (Abel) in Power Rangers Lightspeed Rescue, with the former being groomed, manipulated, and taught to believe that their father loved his sister more than him. He makes a HeelFace Turn eventually
Danny and Patrick Quinn from Primeval. Danny joined the ARC to look for his disappeared brother. He finally meets him in series 4 and is horrified to learn he's become a psychopathic killer.
In Season 7, Lex Luthor ends up creating his own Cain and Abel, when it's revealed he made Grant Gabriel as a clone of his dead baby brother. When Grant discovers this, he becomes very angry and hateful of Lex. Grant tries to form a familial relationship with their father Lionel against Lex's wishes. So Lex hires a hitman to gun him down. Then Lex goes outside to scream in the rain.
Smallville also has a version of Zor-El, Supergirl's father, who is antagonistic towards his brother Jor-El because of his love for Jor-El's wife, Lara.
Lex and Clark Kent have been billed as being in a Cain and Abel relationship since the very first episode it seems.
And in Earth-2, Clark was adopted by Lionel Luthor. Didn't end well for Lex. And father is OK with that because he believes in social darwinism. However, Lionel was furious that his adoptive son hasn't killed him yet, as should be expected. After coming to "our" universe, he's soon began to miss his son and planned to revive "our" Lex. Which he did.
Jor-El and Zod were also similar to Clark and Lex.
Lex ultimately ends up the Cain to yet another sibling — younger half-sister TessMercer, who he murders in the Grand Finale. His reasoning is that it's a version of a Mercy Kill so that she doesn't end up likehim, but few people buy that—he almost definitely killed her so that she was out of his way, since at the time she had control of LuthorCorp.
In Star Trek: The Next Generation, The android Data has a "brother" named Lore, which turned out to contact an alien mass-killer entity and tried to let it kill everyone aboard.
Cain himself appears in Season 9 with a twist. He says that Abel was not speaking with God As the Good Book Says..., but with Lucifer. Desperate to save his brother's soul from Hell, Cain told Lucifer to Take Me Instead. Lucifer accepted Cain's offer, on one condition: if he wanted Abel to get into Heaven so badly, he had to send him there himself. Cain gave Abel his place in Heaven, and became the first Knight of Hell.
Season 11 goes beyond even the show's use of the Trope Namer above, when it reveals that the Darkness is God's sister.
In Supergirl (2015), Kara's mother Alura was the Abel to Astra's Cain. Alura sentenced her own sister Astra to captivity in the Phantom Zone after the latter attempted a coup d'etat.
An episode of Tales from the Crypt, appropriately titled "My Brothers Keeper", involves two conjoined twins, one of whom is a wholesome shy guy, while the other is a vain lectherous douchebag. Needless to say they don't get along.
Terminator: The Sarah Connor Chronicles features an AI version of this with John Henry, who considers the newly emerging Skynet to be his "brother" since they share the same code base. Given the prevalence of Biblical metaphors in this series, it's not surprising that the Cain and Abel comparison is explicitly brought up; John Henry wonders which of the two brothers he is.
In the Brazilian telenovela Trail of Lies, Felix Khoury always resented his adoptive little sister Paloma for taking away part of his future inherance, to the point that he left her to bleed to death after she had a complicated birth in the bathroom of a bar.
Torchwood has Captain Jack and his (in this case younger) brother Gray. Gray is evil because he wants vengeance on Jack for accidentally letting go of him when fleeing from evil torturous creatures when he was little and letting him grow up being constantly tortured by them.
Later subverted as Scorpio reveals in his dying moments that he'd never intended to betray his planet, but became obsessed with the power being an assassin gave him, and he's thankful that Stinger managed to snap him out of it.
Irony, as the actor who played Scorpio also played Takatora from Kamen Rider Gaim, as mentioned above.
Damon (Cain) and Stefan (Abel) Salvatore from The Vampire Diaries, who've been in love with the same girl twice in the past century and a half. Currently subverted in that we've (almost) reconciled and save each other's lives more than they try to kill each other. Also Klaus (Cain) and Elijah (Abel), who parallel Damon and Stefan's relationship.
The Walking Dead has a gender-flipped version of this trope with Mika (Abel) and Lizzie (Cain) Samuels, two young girls who join the main cast in the prison around Season 4. It started out mildly, but then along came the Wham Episode "The Grove", in which Lizzie kills Mika in cold blood with a knife after she completely loses her mind towards the end of the episode. Harmful to Minors, indeed.
The battle between twin brothers Adam and Zachary is the entire premise of The Wanderer.
Wizards of Waverly Place. Although Justin, Alex, and Max all compete to win the absolute Family Wizard title, Justin and Alex are really into it, due to the burning, brotherly hate they have for each other, that grows more and more as episodes pass by. It's a serious case of sibling rivalry, even though it's not clear who is Cain and who is Abel in the relationship. Justin and Alex seem to constantly switch these roles.