The light-hearted nature of Captain Marvel can distract you from the fact that several of his enemies have been quite the omnicidal maniac.
The Ice King sought to envelop Earth in a new Ice Age by freezing the oceans. His success would probably have spelled the end of most life on Earth, humans included.
King Kull, Lord of the Beast-Men, is determined to wipe out humankind in revenge for them killing off his entire species except for himself. When Captain Marvel joined the DCU and many of his rogues' gallery were also revived, Kull observed the occasion with an even more ambitious plan: wipe out humanity, not only on his own version of Earth, but on all Earths, in all universe-timelines throughout the multiverse.
The 52 version of Mister Mind evolved into a monster called the Hyperfly and tried to devour the multiverse.
In one story, Sivana takes a shot at it. Because Captain Marvel prevents Sivana's plan to take over the Rock of Eternity so he can take over the Universe, Sivana tries to activate a Proton Bomb to destroy the Rock of Eternity, which is the Keystone of the Universe and will cause its destruction, even killing himself, deciding if he can't rule the Universe he'll wreck it. He is even laughing at this as he wants one last laugh. Just look at his reaction
Crisis on Infinite Earths: Anti-Monitor, whose stated goal is to rule an Anti-Matter universe after all other universes have been destroyed and he has absorbed the energy from their destruction
Zero Hour: Crisis in Time!: Parallax (Hal Jordan, though the circumstances of it was changed during Green Lantern: Rebirth) and Extant, both laboring under the same agenda of wiping the world out to remake it without many of the tragedies Parallax had endured.
Infinite Crisis: Alexander Luthor and Superboy-Prime, who both want to create their own version of the "perfect Earth" and don't care how many different versions of Earth from other realities they need to use as raw material.
Final Crisis: Darkseid (who, upon discovering he is dying, decides to destroy the entire multiverse) and Mandrakk (who more or less feeds on existence and is on a hunger rampage). Darkseid even provides the trope's image.
Blackest Night: Nekron (An embodiment of death itself, which naturally wants to kill everything)
Dark Nights: Metal: Barbatos, a ruler from the Dark Multiverse where worlds are born out of fears and hope the people make before rotting away into oblivion, recruits seven evil counterparts of Batman in order to bring the DC multiverse into darkness.
The Joker of Earth-22 becoming one of these, systematically killing off every hero, villain and civilian in Gotham City in order to "end the story" and create something else leads directly to the creation of the Batman Who Laughs.
Last Days of the Justice Society: Adolf Hitler becomes this near the end of World War II, when he realizes that he and his Nazi forces are near defeat. Using the Spear of Destiny, Hitler links the fate of the Norse gods' Ragnarok with that of the universe itself, causing everything to go in flames from 1945 onward through a Delayed Ripple Effect.
Braniac-5 pre-Crisis. After being driven mad, he wanted to destroy the entire universe, and stole the Miracle Machine that could do anything the user could envision. He could have easily destroyed the Earth, or even several planets of similar size, but he couldn't envision destruction on the grandiose scale he wanted. So he used the Machine to create something that could, the unstoppableembodiment of hate, Omega. Had this beast actually reached the Machine (and the Legion could do little to even slow it down) Braniac-5's plan would have succeeded; they foiled it when Matter-Eater Lad destroyed the Machine by eating it, but was driven insane in the process.
The Legion's foe Time Trapper has their desires and motivations subject to change alongside their mutable identity but at points, such as in Cosmic Boy, their goal is the erasure of all time between the entropy at the end of the universe they're a personification of and that which came before, thereby erasing everything and everyone who has or ever will exist.
Fenris the Wolf is Destruction personified (and likely an aspect of Destruction of the Endless). His goal is to destroy Creation by attacking the seat of God in Heaven. Lucifer stands in his way.
Fenris is assisted in his endeavor to end all of creation by the gods Abonsam and Bet Jo'gie. Abonsam infused with the essence of Fenris willingly gave his life to perform his greatest trick and ultimately dooming Yggdrasil. Bet fails in her attempt to seduce Charlie and dies by his hands.
The Barrowjane Conspirators to destroy Creation, dethrone God and punish him included Lilith, Sandalphon, The Silk Man and Berim from the Jin En Mok. All had their own reasons for participating: Lilith wanted vengeance against God and Heaven for casting her out of Eden, Sandalphon wins the victory that was denied to Lucifer, The Silk Man wants his own universe and when creation ends the Jin En Mok will finally be reborn as themselves.
The Phantom Stranger: One of the four possible backstories for the Stranger given in his issue of "Secret Origins" features a mad scientist from the future who wants to time travel back to the Big Bang and prevent it from effectively occurring. So not only does he want to destroy the universe, he wants to make sure it never even existed in the first place.
In Reign of Doomsday, Doomslayer puts in motion a plan to blow Earth up, driven by his hatred towards all kinds of living beings.
In Supergirl's Greatest Challenge, Supergirl faces an eldritch abomination (nicknamed Positive Man due to its body composed of positive ions) who wanders arond the universe destroying inhabited worlds out of envy and hatred towards all living creatures.
Doomsday. The name says it all. He's also one of the most primitive examples, he's little more than a frightened but sadistic alien man-child who wants to kill everything that might be a threat to him. And he thinks everything is a threat.
Imperiex from Our Worlds at War, a hive minded mechanical entity, saw its purpose as being the "hollowing" of the universe, destroying the flawed creation and remaking it in a new Big Bang. Ironically, the flaw it detected in the universe was itself, and a massive cooperative effort managed to throw him into the past where he in fact became the Big Bang in the first place, via a Stable Time Loop, a fact which Imperiex realizes the moment before it dies.
The Joker did, in fact, reach this state during Emperor Joker, with his reasoning being that a universe that would spawn something as twisted as he was didn't deserve to exist (and besides reality was falling to pieces from the strain anyways).
Winter of Stormwatch becomes this after he flew an Alien-infested Skywatch space station into the sun to save the world. Being an energy absorber, Winter became one with the sun. Trapped by eternal agony he lures out The Authority so they can finally put an end to his life; when it's deemed impossible to kill him without destroying the sun and ending the world, he became enraged. Disgusted by humanity's cruelty, he yells "Your world does not deserve to live" and lashes out. He's eventually stopped by using the Carrier's technology to seal baby universes and was condemned to burn for billions of years. Later on he's released by the new Doctor and revived in his previous normal state. In the latest Stormwatch issues it was revealed he still holds some of the sun's power.
"The Man Without Hope" (MWH) comes from the future and with his superior technology he's a match for The Authority. The future is grim, blank and full of suffering and he wants to prevent it from happening by ending existence all together. Swift receives knowledge from the mythical "gods" about the dark future and how to prevent it. She mentions how the MWH with all his technology couldn't figure out the problem and fix it. The MWH commits suicide when his plan is ruined by The Authority and a new unknown time line is birthed yet he is still convinced that everyone is screwed. The issue ends with the words "beginning of the end" hinting that the MWH was probably talking about human nature being the problem seeing it's the central theme of the graphic novel, "human on the inside"
Wonder Woman (1942): Adjudicator justifies his actions as judgement on the peoples of whatever world he's currently destroying across the multiverse, but he "judges" the planets before sending minions to test the inhabitants of a handful of the representative versions of the planet and that judgement always calls for the destruction of the planet(s) and its/their inhabitants.
Wonder Woman (2006): Genocide despised sentients, and her goal upon "birth" was the extinction of the human race.
Wonder Woman: Odyssey: Nemesis reasoned that she could only fulfill her purpose by destroying humanity entirely. Given that there are other races capable of committing murder in her universe she would have likely found that her job wasn't yet complete with only humanity destroyed.
