The most iconic villain in Star Wars and one of the most iconic in cinema itself, Darth Vader is well know for his awesome power and the ruthlessness with which he wields it.
Leading his Stormtrooper battalions from the front and mercilessly punishing any failures by his subordinates, Vader has some terrifying kills under his belt. Issued with both his crimson red Lightsaber and the power of the Force which he carries within him, let's list which of Vader's kills were the most shocking, unforgettable, and unforgivable.
10 Admiral Trench
This may have occurred before Anakin Skywalker's official christening as a Sith, but it was a clear shadow of things to come. Late in the Clone Wars, Republic and Separatist forces contested control of the planet Anaxes; Separatist Admiral Trench plotted to detonate a bomb that would blow the planet apart.
Going straight to the source for the deactivation code, Trench initially balks at Skywalker's threats before the Jedi slices off his left arms. After fessing up, Trench shocks Skywalker with his electro-staff, an act which earns him a Lightsaber in his chest. As Trench lays dying, Skywalker glibly quips "Admiral, it was a pleasure," totally tuned out from the violence he's just committed.
9 Tusken Raider Camp
This was the first significant step Anakin took towards the Dark Side, and it was a suitably horrifying one. Tracking his kidnapped mother Shmi to a Tusken Raider encampment, Anakin reunites with her for only a moment before she succumbs to her injuries. In rage and sorrowful at having lost his mother again so soon after finding her, Anakin takes vengeance upon her kidnappers.
He goes a step farther, however, and commits a small scale genocide, wiping out the entire camp, women and children included. The deaths granted Anakin his first taste of the instant gratification the Dark Side would bring, and its an impulse he'd return to many times over.
8 Count Dooku
While not his first brush with the Dark Side, it was this moment at the tail end of the Clone Wars that set Anakin upon an irreversible path towards evil. Defeating and literally disarming Separatist leader/Sith apprentice Count Dooku, Anakin is instructed by the captive Chancellor Palpatine (unbeknownst to the young Jedi, Dooku's master Darth Sidious) to execute Dooku.
In these brief seconds, Dooku's evil vanishes, replaced by a frightened old man who's final thoughts are a realization everything he's fought for will be meaningless. Initially resistant, Anakin cedes to his master-to-be's commands and slices off Dooku's head. The Rule of Two is the Sith's only iron law, and with Dooku's death, Anakin cleared a place for himself.
7 Rebels Aboard The Profundity
As the iron first of the Emperor Palpatine's rule, Vader was frequently tasked with putting down insurrections across the Empire; there's no better example of his merciless efficiency in this task than the Battle of Scarif's conclusion.
Boarding the cruiser Profundity, Vader tracks the Rebels escaping with stolen blueprints to the Death Star and jams their exit nearly shut with his Force powers. Marching down the hall towards the exit, Vader effortlessly deflects the Rebels' blaster bolts and begins slaughtering them one-by-one. A terrifying display of power, if one of the Rebels had been as few as three seconds slower, Vader would've ended the Rebel Alliance in that moment.
6 Eeth Koth
Leaving the Jedi Order before the conclusion of the Clone Wars, Master Eeth Koth escaped Order 66 and fled into hiding. Becoming a priest and marrying, Koth and his new family enjoyed five years of peace before being located by agents of the Empire. Vader and a squad of Imperial Inquisitors arrive just as Koth's wife gives birth to a daughter; Vader is eager to take from Koth what he denied himself.
As the two former Jedi duel, the Inquisitors chase Koth's wife and successfully abduct his daughter. With Koth distracted by the sight of his kidnapped daughter, Vader, without a hint of remorse, stabs and kills the very man he'd once rescued from General Grievous during the Clone Wars.
5 Shaak Ti
The attack of the Jedi Temple was Sidious' first test for his new apprentice; would he destroy the world he'd known up to that point and give himself over to the Dark Side? Horrifyingly, Vader passed with flying colors, butchering numerous Jedi, including ones he'd previously called friends. Among them was the Togruta Master Shaak Ti.
Happening upon her meditating, blissfully unaware of the carnage, Vader hesitated for only a second before stabbing her through the chest with his Lightsaber, not even granting her the mercy of an honorable death. Anakin Skywalker had fought alongside Shaak Ti in the Clone Wars, and to see him cut down a comrade in arms so casually showed how far gone he was even by this early point.
4 Captain Needa
Darth Vader's exceedingly low tolerance for failure was infamous through the ranks of the Imperial Navy; he terrified them much more than any member of the Rebel Alliance. Perhaps Vader's most brutal case of "making an example" of an incompetent officer was Captain Lorth Needa of Star Destroyer Avenger.
Assigned to capture the Millennium Falcon, the Rebel ship evaded its pursuers thanks to some clever thinking from Han Solo. Displaying surprising nobility, Needa accepted full responsibility for the escape and apologized to Vader in person, hoping the Sith would spare his crew. Vader obliged, but still killed the Captain himself with a slow, agonizing Force Choke.
3 Obi-Wan Kenobi
Once Anakin Skywalker's brother, father, and best friend all in one, Obi-Wan Kenobi became an object of pure hate for Darth Vader. It was the former friends' duel on Mustafar which gave Vader the injuries for which he requires constant habitation of his armor, and during the two decades between that duel and their final one, Vader often fantasized about taking vengeance on his former master.
It should come as no surprise that when they met again at last, Vader struck down Kenobi, but seeing the two's relationship end on such a violent note was a tragedy nonetheless.
2 Jedi Younglings
This killing is the single most shocking moment in a Star Wars movie; Vader's cold, machine-like ruthlessness was well-displayed throughout the original trilogy, but he'd never done something as viscerally repugnant as murdering a child onscreen. In Revenge Of The Sith, that's exactly what the newly baptized Sith Lord does.
Vader finds a small group of Jedi toddlers hiding in the Council chambers; seeing only brave Jedi Knight Anakin Skywalker before them, the children plead for his assistance. Vader responds by silently igniting his Lightsaber. This heinous act cemented that Anakin had truly given himself to the Dark Side; indeed, viewing the killing through a security recording is what convinces Obi-Wan that his apprentice is gone.
1 Padmé
The great, tragic irony of Anakin's fall; the woman he was trying to save died as a result of his own actions. Alerted to Anakin's turn by Obi-Wan, Padmé follows her husband to Mustafar and confronts him. She's horrified by his change while Vader is outraged by Obi-Wan's presence; quickly convinced the two are conspiring against him, Vader chokes his wife with the Force, knocking her unconscious.
This is the last time the star-crossed lovers see each other, at least in this life; the trauma, physical and emotional, inflicted by her husband saps Padmé of her will to live and she dies soon afterwards. Learning of his culpability in his love's demise is what breaks Vader, transforming into the blunt instrument of Sidious' will who will spread much more death across the galaxy for the next two decades.