Starfleet's first ever Klingon officer, Captain Worf (Michael Dorn) has killed around 27 Klingons during his history in Star Trek. While commanding the USS Defiant, Worf was even accused of killing 441 Klingon civilians, but this was revealed to be an elaborate deception on the part of the Klingon Empire to discredit Starfleet's highest-profile Klingon officer. For a society that is defined by both combat and honor, it's hardly surprising that Worf racked up some such a high kill count when it came to his fellow Klingons.
In Star Trek: The Next Generation, Worf's service record earned a black mark from Captain Jean-Luc Picard (Patrick Stewart), who objected to Worf killing a fellow Klingon while in Starfleet uniform, regardless of the shared traditions. With one or two notable exceptions, the killings committed by Worf after this onishment were done so in the line of duty. Here are the estimated 22 Klingons that Worf has killed in both Star Trek: The Next Generation and Star Trek: Deep Space Nine.
7 Korris In Star Trek: TNG Season 1, Episode 20, "Heart Of Glory"
Orphaned from a young age, and raised by Humans, Worf was often presented as an outlier in the Klingon Empire. This conflict was at the heart of many of Worf's best Star Trek episodes, and "Heart of Glory" is the earliest example. After they were rescued from their stricken vessel, Worf got to spend time with three Klingon fugitives, who gave him a crash course in his culture. However, when they decided to take the USS Enterprise-D, Worf was forced to choose where his loyalties lay. He eventually chose the Enterprise, when he shot and killed the remaining fugitive, Korris (Vaughn Armstrong) after acknowledging that, perhaps, he wasn't a true Klingon after all.
6 Duras In Star Trek: TNG Season 4, Episode 7, "Reunion"
Worf earned his black mark when he killed prospective Klingon Chancellor, Duras, son of Ja'rod (Patrick Massett), in battle, claiming his right of vengeance. Duras' father, Ja'rod had framed Worf's father for betraying the Klingon Empire to the Romulans, leading to the Khitomer Massacre. When Worf's lover K'Ehleyr (Suzie Plakson) discovered this conspiracy, she was killed by Duras. Under Klingon law, Worf was well within his rights to challenge the murderer of his mate to a duel to the death, which Worf won. It did not fully heal the Klingon's pain, however, nor did it end his problems with the Duras family.
5 Lursa, B'Etor, And Their Crew In Star Trek Generations
It's unclear exactly how many Klingons were serving on the Duras sisters' vessel, but given the on-screen destruction, Worf kills roughly 13 Klingons including Lursa (Barbara March) and B'Etor (Gwyneth Walsh) in Star Trek Generations. The Duras sisters had managed to extract the shield modulation of the Enterprise-D by hacking the VISOR of Lieutenant Commander Geordi La Forge (LeVar Burton). The Enterprise crew was able to turn the tables on the Klingon sisters, however, and it was the job of tactical officer Worf to deliver the death blow against them, almost ending a decades-long feud between their families.
4 The Klingon Boarding Party In Star Trek DS9, Season 4, Episode 1, "The Way of the Warrior"
In the thrilling climax to Worf's first Star Trek: Deep Space Nine episode, "The Way of the Warrior", a full-scale Klingon invasion of DS9 takes place. As the Klingon fleet fire on the station, unnamed Klingon warriors board DS9 to capture the Cardassian officials seeking shelter aboard. Worf and the crew bravely fight the invaders as they wait for Starfleet reinforcements. In the melee, Worf is seen to kill roughly seven of the Klingons that attack DS9's Ops deck, further strengthening his loyalty to the Federation during a fraught period in their relations with the Klingon Empire.
3 Toral's Army In Star Trek: DS9, Season 4, Episode 9, "The Sword of Kahless"
Worf teamed up with Star Trek: TOS Klingon, Kor (John Collicos) and Lt. Commander Jadzia Dax (Terry Farrell) to locate the mythological Sword of Kahless. Unfortunately, Toral, son of Duras (Rick Pasqualone) was also looking for the relic, hoping to fulfill his father's destiny by asserting his place at the head of the Klingon Empire. Worf had previously refused to kill Toral, as the child should not have been punished for his father's crimes. Toral survives his encounter with Worf and Kor, but three of his men are killed by Worf as the group escapes the caves with the valuable artifact.
2 Kurn In Star Trek: DS9, Season 4, Episode 15, "Sons of Mogh"
Worf doesn't kill his brother Kurn (Tony Todd) in the literal sense of the word, despite his dishonored brother's pleas for him to complete the "Mauk-to'Vor" ritual so that Kurn could experience honor in the next life. Worf would have gone through with the ritual if it weren't for the intervention of Dax and Constable Odo (Rene Auberjonois). Realizing that he can't complete the ritual, and that Kurn can't live with the dishonor to the family name caused by Worf's objection to the war with Cardassia, Dax proposed an alternate option for killing Kurn.
He had his brother's memories wiped, his face genetically modified and his DNA re-sequenced so that he would, in essence, become a completely different man. This was a less bloodthirsty means to give Kurn honor in his next life, as he assumed the new identity of Rodek, the fictional son of a Mogh family, friend, Noggra (Robert DoQui). While the ending may have short-changed Worf's brother, it served as a sobering reminder of how disconnected Worf was from the Klingon Empire during their controversial war against the Cardassian Union.
1 Chancellor Gowron In Star Trek: DS9, Season 7, Episode 22, "Tacking Into The Wind"
In an interesting reversal of "Reunion", Worf was again forced to kill a Klingon Chancellor, but this time it was at the suggestion of his commanding officer. Toward the end of Star Trek: Deep Space Nine's Dominion War, Worf was concerned that the egotistical and reckless decisions of Chancellor Gowron (Robert O'Reilly) put the war effort at risk. Captain Benjamin Sisko (Avery Brooks) agreed with Worf's assessment and, in stark contrast to Picard, authorized Worf to use any means necessary to remove Gowron from power.
As the man who effectively put Gowron in power by killing Duras, it was fitting that it was Worf who eventually ended his reign. Challenging the Chancellor for his position, Worf killed his former friend Gowron in a duel, before handing the Chancellorship over to DS9's General Martok (J.G. Hertzler), Worf's friend and revered Klingon war hero. To date, Gowron was the last Klingon that Worf killed in Star Trek, on-screen; however Worf's revelation that he considered sending his former Enterprise-D crew mates the heads of his many enemies suggests that he's killed more Klingons in the interim decades.