From the very first scenes of A New Hope, it was clear that droids were going to be a big part of the Star Wars franchise. R2-D2's heroic commitment to his duty has saved multiple characters, and C3-P0's comedic relief also played an important part in the film. Of course, they both went on to be franchise staples and were the only characters to appear in every Star Wars film (except for Solo: A Star Wars Story).
However, not all droids were as helpful and heroic as R2 and 3P0. In fact, some of them were downright antagonistic and ruthless. The Trade Federation's B1 Battle Droids were intentionally stupid cannon fodder, but other droids were extremely lethal, super deadly and even capable of killing Jedi. So, here's a look at the deadliest droids in Star Wars.
Mister Bones Was a Literal Nightmare
Mister Bones is in LEGO Star Wars: The Skywalker Saga, but up until then, his only appearance was in Chuck Wendig's Aftermath trilogy. Bones had the frame of a B1 Battle Droid, but his maker, Temmin Wexley, heavily modified the droid to be his personal body guard. He also gave Bones a murderous and sadistic personality -- to the point where Bones would literally sing and dance like Pennywise the Clown while he killed his victims. Bones had a vibroblade for an arm, but what made him especially deadly was the fact that Temmin downloaded various combat programs into Bones including: martial arts videos, the movement style of General Grievous, and the body-mapped maneuvers of Ryloth la-ley dancers.
IG-88 Was the Original Killer Droid
First seen in The Empire Strikes Back, IG-88 was one of the deadliest bounty hunters in the galaxy. He was a rouge assassin droid that turned on his makers, killed them and became his own master. Over the years, it had quite the rivalry with Boba Fett. The deadly droid had a whole arsenal of weapons including: blaster rifles and pulse canons, a neural inhibitor, a poison dart gun, a flamethrower, a sonic device, toxic gas dispensers, concussion discs and a vibroblade. Basically, if there was a Terminator in Star Wars, it would be IG-88.
0-0-0 Was a Torture-Loving Protocol Droid
0-0-0 originated as the Triple-Zero protocol personality matrix, but was quarantined for centuries. Years later, Darth Vader and Doctor Aphra stole the personality matrix and installed it into a protocol droid called 0-0-0. When the droid woke up, he introduced himself as specializing "in etiquette, customs, translation and torture." That's pretty terrifying because his hands might as well have been a Swiss Army Knife.
Magna Guards Were Some High-Class Security
The IG-100 MagnaGuards were first seen in Revenge of the Sith, and their skill can also be seen in The Clone Wars. They regularly accompanied General Grievous and other high-ranking Separatist leaders because they were more than a match for most Jedi. Armed with electrostaffs, one Magna Guard would occupy an enemy while its partner would try to outflank the adversary. The droids were also notorious for being able to continue fighting after losing limbs... and even their heads.
HK-47 Had a Thing for Killing Jedi
Constructed by the Sith Lord Revan, HK-47 was a Hunter-Killer series assassin droid, who specialized in Jedi hunting. He was proficient with the use of blasters, but because he fought against Jedi, he was also equipped with grenades, sonic screamers, cluster rockets, plasma charges and poison gas. Eventually, he didn't complete a mission, and because of that, he couldn't remember his master. So, he wandered the galaxy slaughtering new master after new master and proving himself a true menace. He may no longer be canon, but he can still be seen in Star Wars: Galaxy of Heroes.
JK-13 Security Droids Were Force-Sensitive
Like HK-47, the JK-13 security droids are no longer canon, but they were particularly terrifying in Legends. Appearing in a novel called Star Wars: The Cestus Deception, the JK-13s definitely earned their nicknames as "Jedi Killers." They looked like giant spiders, and for weapons, the JK-13s would send out tentacles that could cut or deliver an electric charge. They were also equipped with their own shield generators that could deflect energy-based weapons. More importantly, though, each JK-13 housed a creature known as a dashta eel, which were Force-sensitive. That, in turn, gave the droids some measure of precognitive abilities, which allowed them to counter Jedi attacks.