It's kind of a lesser-known fact that Goku, over the course of Dragon Ball Z, only killed two villains. Goku has a tendency to spare the lives of his enemies, a move that usually works in his favor, since most of his friends are former opponents. But, this doesn't mean that he isn't a killer. He killed the aforementioned two villains in Dragon Ball Z, but he also murdered a ton of people when he was just a kid in Dragon Ball.
Fans might think of Goku as a kind-hearted warrior, one who defies the nature of his cold-blooded heritage. This might be true to an extent, he's definitely not malicious, but his childhood head trauma didn't completely knock out his murderous instincts. The craziest part is that most of the time Goku killed, it when he was just a kid! He surprisingly got better at not murdering people in Dragon Ball Z, but that doesn't mean he's completely innocent. It's not like he's got a body count close to Vegeta -- that dude's a straight up mass murderer -- but Goku has definitely caused his fair share of deaths. If you think everyone's favorite Saiyan is truly a "good guy," then here are the 15 times that Goku killed.
15 HIS GRANDPA
Goku's first victim was the very same man who raised him, his adoptive Grandpa, Gohan. Son Gohan found Goku as an infant, surprised to find the child had a tail, unaware of the dangers that came with it. Before we learned that it was Goku himself, the monkey-tailed child told the story of a monster coming out on a full moon and squashing his grandpa under his mighty foot.
We would soon come to learn that Goku was the monster that killed his grandpa when he turned into a great ape on the full moon. However, Goku himself wouldn't know he caused his grandpa's death until he fought Vegeta, completely unaware of his transformation for most of his life. It might not have been intentional, but Goku is still responsible for Grandpa Gohan's death.
14 RED RIBBON SOLDIERS
The Red Ribbon Army served as the main antagonists for a few sagas of the original Dragon Ball manga and anime. They were a paramilitary organization comprised of criminals, led by Commander Red, who were always after the dragon balls, and were willing to find them by any means necessary. In their attempts to wish for world domination, they sent countless soldiers to achieve their goal.
On the multiple occasions that Goku faced this army to stop their plans, he ends up killing his way through most of their soldiers. Goku uses his super strength to crush, throw and punch most of these lowly peons to their graves. To be fair, Goku might not have fully developed his heroic aversion to killing by this point, but it's still messed up that a little kid killed so many people.
13 BUYON
Foot soldiers weren't the only weapons that the Red Ribbon Army used in his mission to get the Dragon Balls; there was also Buyon. Buyon was General White's "secret weapon," a giant, pink, blubbery alien with crazy fighting techniques. The pink alien was able to use his tongue to attack, deflect attack with his rubbery exterior and fire energy waves from his antenna.
However, none of this was enough to stop his defeat at the hands of Goku. After a long struggle, Goku murdered the alien beast by exposing him to cold and shattering him with a super strong kick. To be fair, Goku probably didn't have any choice but to kill Buyon, since the alien monster would have most likely devoured or killed him.
12 CAPTAIN YELLOW
Captain Yellow was one of the few soldiers under Commander Red who got a good amount of time in the spotlight. Yellow is an anthropomorphic tiger who pilots a plane for the Red Ribbon Army. When we first meet him, he's attempting to steal a dragon ball from the Korin village, but Goku shows up to stop him.
Captain Yellow takes a hostage to the skies to barter for the dragon ball, a villainous act that Goku plans to stop. While in midair, Goku arrives on his flying nimbus to take out the evil tiger pilot. In a lethal attack, Goku punches Yellow out of his plane which causes the soldier to fall to his painful death. Goku might not have intended for Yellow to die, but he got what he deserved!
11 NINJA MURASAKI
The Red Ribbon army's headquarters was known as Muscle Tower. It was located in the snowy Jingle village and served as residence for high ranking officers of the criminal organization. The highest ranking general in the tower was General White, with the second in command being Ninja Murasaki. Ninja Murasaki was an overconfident, but cowardly ninja who faced Goku firsthand.
Though he might've been clumsy and oafish, Murasaki was the first Red Ribbon Soldier who took more than a single episode to beat. He also survived the fall of Muscle tower and an avalanche caused by Goku's kamehameha. His eventual demise came by accident when Goku unintentionally threw a bomb in his direction, blowing up the ninja in what we can only imagine was a painful and gruesome death.
10 OFFICER BLACK
The commander of the Red Ribbon Army, Commander Red built the army under the guise of getting the dragon balls for world domination. This was all a ruse, as Commander Red really wanted the dragon balls so he could wish himself taller. After learning of this secret, his most loyal follower, Officer Black, killed him and took over the Red Ribbon Army.
Commander Black renamed the army the Black Ribbon Army and offered the incredibly strong Goku a position in his new world order. But our hero refused, leading Black to attack him in his Battle Jacket. This mechanized suit puts him on the same level as Goku, and they fight. Goku wins in the end by punching the suit, causing it to explode with Black still in it.
9 TAMBOURINE
After King Piccolo was released by Emperor Pilaf, he created four mutated sons, Tambourine was one of them. These Namekians were unlike any other, with Tambourine lacking antenna in his winged, gargoyle-like appearance. Goku Eventually defeated Tambourine, killing the alien mutant. But, this murder wasn't in cold blood, since Tambourine's favorite "hobby" was killing humans and he had to be stopped.
Goku originally faced Tambourine after he killed Krillin. He was out for revenge for his fallen friend, but was weak from a previous fight. Because of this, Tambourine quickly defeated Goku. After this easy defeat, Tambourine faced Goku confidently in a rematch, but Goku was much more prepared this time around. After Goku got the upper hand and viciously beat Tambourine, the alien attempted to flee the fight, but Goku killed him with a kamehameha blast.
8 DRUM
Like his "brother" before him, Drum also fell victim to Goku, but his death was much quicker. Drum was one of King Piccolo's four mutated sons, appearing similar to Tambourine, but much larger and without the wings. This ogre-like Namekian was considered to be the strongest of his brothers due to his large stature and high power level.
However, this didn't save him from being killed by Goku in one of the most gruesome ways possible. When Drum was about to kill Tien, Goku showed up in the nick of time, attacking with a flying kick. This initial kick stunned Drum, and with a second powerful kick, Goku knocked the Namekian's head right off, causing his eyes to pop from his head in a bloody, gruesome death.
7 KING PICCOLO
King Piccolo's other mutated sons, Cymbal and Piano, were eventually killed as well. Yajirobe killed and ate Cymbal, and Piano was killed by the collateral damage of Goku's battle with King Piccolo. This fight also resulted in Piccolo's death, though we all know that he would later be reincarnated into Piccolo Jr. Regardless, this fight was absolutely insane, and King Piccolo's death is even crazier.
Goku didn't hesitate to kill in his childhood, and the evil demon king had to be stopped, which is why Goku finished him off for good. In their battle, Goku killed the demon king by using the "Penatrate!" technique, which consisted of Goku shooting a Kamehameha at the ground to propel himself forward with such great force that he punched his way clean through King Piccolo. Talk about overkill!
6 RADITZ AND HIMSELF
The first villain of Dragon Ball Z was Goku's long lost brother Raditz. He was also the first villain of Dragon Ball Z that Goku technically killed. Though he has an involvement in Raditz's death, Goku did not directly kill his brother. After showing up on Earth and challenging Goku, Raditz proved to be a powerful opponent, requiring the combined efforts of Goku, Gohan and Piccolo to defeat him.
Goku temporarly gained the upper hand by grabbing Raditz's tail, and Gohan helped out by angrily flying straight into his uncle. But, it wasn't enough. Goku assisted in finally defeating his brother once and for all by holding him in place as Piccolo fired his special beam cannon. The blast killed them both instantly, Goku sacrificing himself to kill his evil brother.
5 KING KAI, BUBBLES AND GREGORY
Goku has killed a lot of people in his life, but all of them were bad guys... up to this point that is. Though it wasn't exactly a murder, Goku is directly responsible for the deaths of King Kai, his pet monkey, Bubbles, and his cricket friend, Gregory. This was, of course, a way to prevent the deaths of everyone on Earth, but it still counts.
After Gohan defeated Cell, the villain, for lack of a better term, coughed up Android 18 and reverted to his semi-perfect form. Being a sore loser, Cell set his body to explode and destroy the whole Earth. But, at the last minute, Goku used instant transmission to teleport Cell to King Kai's planet, killing himself, King Kai, Bubbles and Gregory in the explosion.
4 YAKON
Yakon was the first villain that Goku directly killed in Dragon Ball Z, one of only two. Yakon was one of the enemies the Z-fighters faced in Babidi's spaceship, a minion of the alien wizard. Yakon is apparently one of the most feared and powerful beings in his area of the universe, a powerful monster who wants to eat the Z-fighters.
Yakon's special ability is that he can devour light, a convenient power that allows him to absorb the energy and shoot it back in a powerful blast. Yakon thinks that this power will give him the advantage over the glowing power of Goku's Super Saiyan forms, and it does at first. However, Goku uses Yakon's appetite for light to his advantage by overfeeding him his energy until the alien explodes from overindulgence.
3 KID BUU
The only other villain that Goku killed throughout the run of Dragon Ball was the final form of Buu, aka Kid Buu. Then again, since the energy that Goku used to create the spirit bomb that destroyed Buu was gathered from the people of Earth, you could also argue that every being on Earth is responsible for defeating the alien menace.
That said, Goku was the one who gathered the power and launched the final attack, so he is the one who officially killed Buu. After Vegeta helped to distract the villain while Goku could make the spirit bomb, the final attack was launched and Kid Buu was destroyed once and for all. This final fight marked the end of Dragon Ball Z, and Goku killing Buu with a massive spirit bomb was an epic battle to finish off the series
2 FRIEZA
In thier original fight on Namek, Goku's Super Saiyan form gave him the upper hand against Frieza. Goku was able to defeat the villain just before the planet was set to blow. Even though he was cut in half, Frieza didn't die, and Goku wouldn't finish him off. In fact, Goku gave Frieza some of his energy to he could get to safety before Namek's destruction. This turned out the be a mistake as Frieza was saved by his father and given cyborg enhancements.
Goku wasn't as foolish the second time around... sort off. Though Frieza first died at the hands of Trunks, he was eventually wished back to life by his underlings in both Resurrection F and Dragon Ball Super. After Frieza destroyed the Earth during his fight with Vegeta, Whis turned back time so that Goku could kill Frieza with a god kamehameha.
1 CITIZENS OF EARTH (GOKU BLACK)
This one is kind of a technicality, but it's still worth mentioning. In an alternate timeline, Future Trunks and the citizens of Earth are terrorized by Goku Black. Black is actually Supreme Kai Zamasu in Goku's body. In this body, Goku has killed countless people, turning Goku into a bigger mass murderer than Vegeta, at least by proxy.
Goku Black kills humans as part of his Zero Humans Plan, an attempt to rid the universe of mortals that he's deemed unnecessary and primitive. After switching bodies with Goku using the Super Dragon Balls, Zamasu killed Goku, Chi-Chi, Goten and most of the Z-Fighters. Perhaps the most horrific part of all this is that the Son family was killed by Goku's body, as were all his friends.