Thanos acquiring all six Infinity Stones and snapping half of life from existence is the supervillain's single greatest accomplishment in the pages of Marvel Comics. However, it wasn't his first plan with the powerful, reality-changing objects. Originally, the Mad Titan had a completely different and even deadlier idea for when he obtained all of the Infinity Stones: to destroy all the stars in the cosmos.
In The Infinity Gauntlet saga by Jim Starlin, George Perez, and Ron Lim, as well as in the Avengers films in the Marvel Cinematic Universe, Thanos' ultimate quest was to acquire all of the Infinity Stones to snap half of all living beings from existence. His motivations for doing so in each of the tellings were quite different. In the comics, Thanos wanted to erase half of all life to please the living embodiment of Death - whose attention he desperately sought. In the MCU, the Mad Titan wanted to snap half of life to restore balance in the universe. However, before he ever put the Infinity Stones into his Infinity Gauntlet, he first tried to use them in another way entirely.
More than a decade before the Infinity Gauntlet saga was published, Thanos sought out all six Infinity Stones in Avengers: Annual #7 by Starlin, Josef Rubinstein, Petra Goldberg, and Tom Orzechowski. In the story, Adam Warlock warns the Avengers that Thanos has survived their last battle and has a new scheme to win the hand of Death. When Warlock is asked what Thanos is planning he tells the heroes that he plans on "blowing every star out of the heavens."
Thanos actually manages to acquire five of the Infinity Stones, as he finds them scattered across the universe, including finding one on the Earth's moon and stealing one from the cosmic being The Stranger. Thanos would siphon the sixth stone off of Warlock's head during a battle with Magus. Thanos would use the Infinity Stone's properties to create a massive synthetic gem. Ultimately, the egg is destroyed by Iron Man.
Destroying all the stars in the universe would have caused mass death across the cosmos that would be pretty much unrivaled. On Earth, almost every single living thing (that didn't have the powers to fly in space) would instantly die without the sun. In the end, Thanos' first attempt to use the Infinity Stones to impress Death failed before his plan could be fully put in place. Thanos would learn from his mistake and the next time he acquired all six stones, he would make sure to use them before Marvel's greatest heroes could foil his deadly ploy.