#ComicBytes: Five times the Man of Steel intentionally killed someone
What's the story
Superman, the alien Kal-El from Krypton, is a beloved superhero of DC. Apart from his many heroic qualities, Superman has a no-kill code, which is great for his adversaries. However, he doesn't always stick to that rule. Over the years, Superman has ended multiple lives. While many of these incidents were due to mind control, here are the times when he intentionally killed someone.
Zod
Finished off Zod and his allies with Green Kryptonite
In Superman Vol. 2 #22, the Post-Crisis Superman, along with Supergirl, Lex Luthor, and his resistance team, confronted Zod and his associates, Quex-UI and Zaora, in a Pocket Dimension for killing almost every human being on that universe's Earth. To prevent the genocide in this dimension to reach his universe's Earth, Superman killed Zod's team by exposing them to Green Kryptonite.
The Joker
Impaled the Joker for killing Lois Lane, his unborn child
In Injustice: Gods Among Us #2, the Joker kidnapped a pregnant Lois Lane and made her heart a trigger to a bomb implanted to destroy Metropolis. When Superman reached to save her, he accidentally killed her due to severe hallucination from Scarecrow's toxins. Her death also triggered the bomb. After losing Lois, his unborn child, and his city, an outraged Superman impaled the Joker.
Imperiex-Braniac
Destroyed Imperiex and Brainiac by sending them back in time
In Trial by Fire: Action Comics #782, an alliance of superheroes and villains fought Imperiex and Brainiac to save the universe. Combining Lex's displacement technology, Darkseid's Boom Tube, Tempest and the Amazons' magic, and Steel's new armor, the alliance created a portal to the past. Using this, Superman sent the two villains to the exact moment of the Big Bang, where they were destroyed.
Mister Mxyzptlk
Trapped Mister Mxyzptlk between two dimensions to rip him apart
In Whatever Happened to the Man of Tomorrow? Mister Mxyzptlk, a nuisance from the fifth dimension, became a true villain and orchestrated attacks on Superman. As the two rivals start fighting, Superman decided to use the Phantom Zone projector. Seeing this, Mxyzptlk tried to escape to his own dimension, but Superman activated the projector to trap Mxyzptlk between two dimensions, which ripped him apart.
Doomsday
Killed Doomsday before dying in front of Daily Planet
In the Death of Superman storyline (Superman Vol. 2 #75), Superman and Doomsday fought till death in Metropolis, in front of the Daily Planet. To save the city from Doomsday, Superman had to kill him, so he snapped his neck. However, he also got fatally injured at the same time. As the name of the storyline says, this was the death of Superman.