As sister to Lursa, B'Etor was one of the Duras sisters responsible for the start of the Klingon Civil War in early-2368. She was the younger sister, the more seductive (and more promiscuous) of the two. She and Lursa supported their nephew Toral as the new Chancellor of the Klingon High Council. Toral was the illegitimate son of their brother Duras. She staked Toral's claim just as Jean-Luc Picard, who was the Arbiter of Succession, was about to pronounce Gowron as Chancellor. In determining their claim, Picard went planet-side and paid an invited visit to B'Etor and Lursa. B'Etor attempted to convince him that Toral's challenge must be approved. B'Etor made a futile effort to seduce Picard. (TNG: "Redemption")
When Picard designated Gowron as the rightful Chancellor, she and her sister took up arms against Gowron. They were supported by the Romulan Empire, who wished to see the alliance between the Federation and Klingon Empire fall apart. They kidnapped Worf and B'Etor took a liking to him and offered herself as a mate to him in exchange for his cooperation. He declined. B'Etor and her sister's plot failed due to a Federation blockade of Romulan ships, which denied them aid and supplies. It more importantly exposed their alliance with the Romulans who most Klingons hated. This caused B'Etor and her sister's support to erode. (TNG: "Redemption II")
The Duras sisters were also responsible for selling bilitrium to Bajoran Kohn-Ma terrorists in 2369. In order to raise capital to rebuild their forces, they offered the Bajoran Kohn-Ma terrorist Tahna Los bilitrium in return for gold-pressed latinum while plotting to sell him out to Elim Garak and the Cardassians once they were paid off. (DS9: "Past Prologue")
Another capital-raising scheme had them seizing a Pakled magnesite mine on Kalla III, overseen by the Dopterian Gorta, and selling its explosive ore to an Yridian, Yog. B'Etor and her sister were also falsely accused of an attempted murder of the members of the Mogh family in 2370. (TNG: "Firstborn")
In 2371, the sisters worked with the El-Aurian scientist Tolian Soran and raided a Romulan outpost to acquire trilithium in exchange for Soran's trilithium bomb. In a recurring theme, she appeared interested in "initiating a mating ritual" with Soran. She was killed in orbit of Veridian III when her Bird-of-Prey was destroyed in a battle against the USS Enterprise-D. (Star Trek Generations)
"This is not a threat, Captain. Just an unfortunate truth."
"So why be our enemy, when you can be our friend?"
"You have manipulated the circumstances with the skill of a Romulan."
"I think he'll find our offer appealing."
"I'll make sure he does."
"Toral is Duras' only son, and he will be the leader of the Council. In your heart, even you know that. But Toral needs guidance."
"A firm hand."
"A father figure. That could be you, if you were mated to B'Etor."
"The rewards could be greater than you can imagine."
"I hope for your sake you were initiating a mating ritual."
- - B'Etor, after Tolian Soran punched her (Star Trek Generations)
B'Etor was played by actress Gwynyth Walsh.
The script for "Redemption" states the pronunciation of B'Etor's name as "be-TOR". Of the scene in which Lursa and B'Etor are introduced, it describes, "B'Etor is several years younger, and more volatile than her sister. [...] B'Etor moves to stand beside Toral. She's not afraid of Gowron and her presence shores up Toral a little." 
The script for "Firstborn" also describes B'Etor as having a, "grating squawk.". 
Makeup designer Michael Westmore made attempts at making Lursa and B'Etor's cranial ridges similar, indicating they were from the same house. "Especially in later episodes of The Next Generation, when Worf's brother Kurn and their rival Duras were stirring up the Empire and Gowron took the throne, I was able to work out family facial styles." Westmore recalled, "The Duras family and the terrible sisters Lursa and B'Etor had the same general features as Duras. What worked for Duras worked for Toral, Duras's son." (Star Trek: Aliens & Artifacts, pp.66-67)
Costume designer Robert Blackman was responsible for designing Lursa and B'Etor's Klingon uniform, incorporating a revealing bustline that was quickly referred to by fans as, "Klingon kleavage". Neither Barbara March or Gwynyth Walsh used chest padding. (Star Trek: The Next Generation Companion, p.169)
Lursa and B'Etor's appearance in "Past Prologue" was included on the suggestion of Star Trek: Deep Space Nine producer Michael Piller to tie the series into established continuity. "The creative synergy allows you incredible opportunities," Piller commented, "It's interesting how we used them. Essentially, we had a story and, in the case of Lursa and B'Etor we said, 'Hey, we've got a real kind of Casablanca spy story and we need someone really be doing double dealings and bringing money and doing gun exchanges; why don't we use the Klingons - and use those characters that we love so much?' It works out just fine to use those guys because then there's a connection and an identification. There's a backstory, there's a history, and all of these things make for a much richer series." (Star Trek: Deep Space Nine Companion, p. 22; Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p.42)
Of her Deep Space Nine appearance, Walsh recalled, "I think they brought us back because it was time. It was fine. It was lovely to work with Rene [Auberjonois], but we mostly worked just by ourselves in that one. We didn't have that much interaction with anyone else. But it was largely the same crew - a lot of the crew had left ST:TNG for ST:DS9 - so it was nice to see some old buddies". ("Double Trouble", Star Trek Monthly, issue 36)
Both Lursa and B'Etor return to Deep Space 9 in the Pocket DS9 novel The Big Game, in order to participate in a poker tournament to raise funds for their war against the Empire. The two attempt to win the tournament by cheating, but when Quark discovers their special deck, it is tossed aside and new one used in its place. Afterwards the two women are quickly defeated by the remaining players.