Service in Starfleet demands a lot from Star Trek's heroes. While some rise to the challenge or are lucky enough to cheat death, many are not so fortunate. Star Trek: Strange New Worlds even features an episode marking Starfleet Remembrance Day, a tribute to those who have lost their lives exploring the final frontier.
While some losses are due to alien attacks or accidents, there are those who make sacrifices in the line of duty. While sometimes these acts are small (Uhura merely sacrifices her dignity in Star Trek 5: The Final Frontier) and some are more existential than physical, they represent the selflessness of Starfleet's best.
10 Trip Tucker
Although the finale of Star Trek: Enterprise was designed as a love-letter to fans, its reception was overwhelmingly poor. From framing the episode's events as part of a holodeck simulation to failing to develop its cast, it's no surprise that T'Pol actress Jolene Blalock called the finale "appalling". Yet the episode's most egregious issue involves its handling of engineer Trip Tucker, whose heroic sacrifice looks more like a pointless death.
Tucker's demise (he sacrifices himself to protect Archer from marauding aliens) is so unconvincing that Star Trek novelists quickly retconned it into a hoax, designed to cover up Tucker's involvement with the mysterious Section 31. For those who prefer to rely on televised Trek, however, Tucker's sacrifice represents the nadir of an already woeful finale.
9 Will Decker
A precursor to the similarly named Will Riker of Star Trek: The Next Generation fame, Will Decker's time in command of the Starship Enterprise during Star Trek: The Motion Picture sees him come into conflict with James T. Kirk, who captained the vessel prior to Decker. Kirk resents Decker's youth and inexperience, while Decker believes that Kirk is ill-equipped to handle the newly refitted starship.
Decker is able to prove himself to Kirk, however. When the sentient machine V'ger possesses Decker's lover, Ilia, Decker chooses to give up his human form to be with her. He joins with V'ger and Ilia, evolving into a new lifeform in the process and ending the threat posed by the machine.
8 Kes
The Ocampan Kes is somewhat overshadowed by her replacement aboard the USS Voyager, the memorable Seven of Nine. This is unfair, as Kes stars in some strong episodes of Star Trek: Voyager, including the time-bending "Before and After" and alien possession tale "Warlord", in which Kes actress Jennifer Lien delivers a bombastic performance.
Kes's telepathic powers continue to grow during her time on the series. However, their development soon endangers the starship. Kes chooses to leave Voyager in a shuttlecraft to complete her transformation, sacrificing the only life she knows to protect the people she cares for.
7 Tuvix
Sacrifices are not always made willingly, as any Aztec victim is likely to know. This is certainly true for Tuvix, a transporter-created hybrid of Voyager's uptight Vulcan Tuvok and the irritating Talaxian Neelix. Although a fusion of two diametrically opposed individuals, Tuvix is a fully sentient individual in his own right—at least until Captain Janeway has him forcibly separated again.
Janeway's treatment of Tuvix continues to divide fans, with some calling her a murderer for her actions. However, Tuvix's enforced sacrifice is not entirely in vain, as it does restore two of Voyager's crew to their proper forms. Star Trek often claims that the needs of the many outweigh the needs of the one, and this may be true in the case of Tuvix.
6 Sylvia Tilly
Science officer Sylvia Tilly provides a much-needed burst of optimism to the gritty Star Trek: Discovery. Tilly's enthusiasm is a throwback to a brighter, more utopian era of the franchise, but this doesn't mean that the character has an easy life. An overbearing mother threatens Tilly's self-esteem, while the Starship Discovery's deadly adventures often put her in danger.
Tilly and the rest of the Discovery crew choose to travel to the distant future in order to stop a sentient machine from destroying the universe. While this is a sacrifice that affects everybody aboard (including series lead Michael Burnham), it is arguably Tilly who has the most to lose by leaving the 23rd century. Burnham has few ties to the era, whereas Tilly leaves behind her family—even if she struggles to get along with them at the best of times.
5 James T. Kirk
James T. Kirk cheats death on many occasions throughout the Star Trek franchise, and even his apparently fatal sacrifice does not actually kill him. When the newly built Enterprise-B encounters the Nexus, an energy anomaly, Kirk volunteers to modify the starship's deflector shield in order to protect the crew. Although he is successful, Kirk is sucked into the Nexus and assumed dead.
In fact, Kirk continues to live in the Nexus until an encounter with Jean-Luc Picard nearly 80 years later. The two men work to defeat Soren, a mad scientist, although Kirk is killed in the process. Actor William Shatner was so dissatisfied with Kirk's demise that he co-wrote a series of Star Trek novels in which a resurrected Kirk defeats the Borg. While these books are generally regarded as a non-canon vanity project, they demonstrate that even multiple deaths can't get in the way of Kirk's adventuring (or possibly Shatner's ego).
4 Worf
While early episodes of TNG found little for Worf to do, later deep dives into the Klingon's internal conflict surrounding his identity yielded some excellent moments. One of these takes place in the two-part "Redemption", in which Worf is given the honor of executing Toral, a Klingon rebel leader.
Although Toral is partially responsible for colluding with the Romulans and starting the Klingon Civil War, Worf spares the boy's life. Ironically, this act of mercy is a form of sacrifice, as Worf denies his Klingon nature and loses the respect of his peers in order to adhere to the Federation's ideals.
3 Benjamin Sisko
Benjamin Sisko suffers a lot during Star Trek: Deep Space Nine. His wife is killed in the pilot's opening minutes, while his role as a spiritual leader to the Bajoran people leaves him torn between his commitments to them and to Starfleet. Sisko's relationship with the Prophets leads to him joining them in the show's finale, a sacrifice in itself, as it takes him away from his family.
Yet Sisko's greatest sacrifice is existential, not physical. With the Dominion overwhelming the Federation Alliance, Sisko sacrifices his Starfleet convictions to convince the Romulans to join the war on his side. Sisko recognizes that this is a necessary evil, although it is unclear if he will ever truly forgive himself for his part in the deception.
2 Spock
Spock is one of science fiction's most famous characters, so it's no surprise that his heroic sacrifice in Star Trek 2: The Wrath of Khan is also regarded as one of the genre's most iconic deaths. When the Enterprise's engines are heavily damaged during a skirmish, Spock enters a radiation-soaked area to make the necessary repairs. This saves the ship, but at the cost of Spock's life.
However, Spock's death (included at the behest of Leonard Nimoy) does not last long. Nimoy's positive experience working on The Wrath of Khan revitalized his relationship with the franchise, resulting in Spock's resurrection in the aptly titled Star Trek 3: The Search for Spock.
1 Christopher Pike
Many in Starfleet have made impulsive, spur-of-the-moment sacrifices. Few, however, have glimpsed their future destiny, and elected to face their fate regardless. Christopher Pike first learns of the sacrifice he will make when visiting the Klingon moon of Boreth; the planet's time crystals show him that he will be horribly injured while saving some Starfleet cadets from Delta radiation.
Pike is understandably haunted by this foreknowledge, and even attempts to avert it. However, he does embrace his fate, although it leaves him horribly disfigured. Despite his suffering, Pike is rewarded for his sacrifice by the powerful Talosians, who offer him a normal existence within one of their ultra-realistic illusions.