If you were a reader of Bronze Age comics, then you've probably run across a few stories featuring the doomed world of
Counter-Earth--a duplicate of our own Earth which was positioned in orbit on the far side of the sun, created with the best of intentions by the High Evolutionary in order to be home to a race of humanity which had none of the violent tendencies of those populating our own world (which is where I suppose the "counter" in its name comes from). Introduced in
the origin story of the character who came to be known as (Adam) Warlock, we watched in shock and sadness as one of the Evolutionary's earlier creations, the vengeful Man-Beast, took advantage of the Evolutionary's lapse into a deep sleep after his labors to board the scientist's moonship and unravel his work by introducing the savage traits of our own species to those on the Evolutionary's new world--a world that the Man-Beast now declared "beyond redemption."
With the Evolutionary poised to destroy his work in order to erase the tragedy of a second Earth now a violent mirror of the first, Warlock, a witness to the travesty, offered to do what he could to fight the Man-Beast's influence on this world and prove to the Evolutionary that this race was deserving of life. The bargain was accepted, and Warlock succeeded in at least bringing an end to the Man-Beast. (Or so he believed at the time.)
In the interim, we were treated to several stories in other titles that involved the humans of Counter-Earth--the Hulk having the occasion to encounter that Earth's Bruce Banner, and, later, being helpless to save Warlock from falling into the hands of the Man-Beast and being put to death (or so it seemed). Counter-Earth also found itself vulnerable to a certain world-ravager whom the High Evolutionary met in defiance:

Over the years, we've seen other instances of Counter-Earths take their place in comics lore. If I remember correctly (I wasn't exactly enamored with stories having to do with Onslaught), the "pocket dimension" created by Franklin Richards to shunt those heroes who sacrificed their lives meeting the attack of Onslaught housed a planet that was given the name "Counter-Earth," a world eventually brought into our universe and renamed "Planet Doom" (after the good Doctor) and later visited by the Thunderbolts. In addition, the Evolutionary took another crack at creating another Counter-Earth--this one inhabited by his New Men (though they'd find the Evolutionary less of a benefactor), while at one time even attempting to merge his creation with our own Earth.
But as for the first world to be known as Counter-Earth--well, we did, regrettably, use the word "doomed" in its introduction, to be sure.
Which dooms us to explore yet another
Marvel Trivia Question
What was the fate of the original Counter-Earth?