9. General Zod, Quex-Ul And Zaora - Superman #22
Not too long after his origin, abilities and nature were rebooted in Crisis of Infinite Earths, Superman was placed in the uncomfortable position of having to kill to save countless lives. A lot of fans are aware of the DCEU version of Superman killing Zod in Man of Steel, but few know of the first time the Last Son of Krypton fatally lived up to this particular moniker.
Through the machinations of the Time Trapper, the mainstream Superman encounters his younger version from a pocket universe that was similar to the Pre-Crisis. This meant that Superboy and all Kryptonians from his time were significantly more powerful than Clark and the latter got first-hand experience of this when he encountered that time’s General Zod, Quex-Ul and Zaora.
The villainous trio went on a destructive rampage throughout the alternate timeline and Superman was forced to intervene after his counterpart had died earlier on. Ultimately, the hero depowered and killed the rogue aliens using a combination of gold and green Kryptonite, respectively (Kryptonite from a universe other than his own has no affect on Superman).
While the pocket universe was spared, the execution weighed heavily on the hero, who up until this point had not taken a life.