With or without the Infinity Gauntlet, Thanos is one of the most deadly and powerful villains in the entire Marvel Universe, and he's usually capable of defeating almost any hero in combat. But while he's usually portrayed as a cruel murderer and monster with universe-conquering intentions, at least one version of the character secretly became the most important hero in the history of his entire reality.
In the 2003 miniseries Marvel: The End by Jim Starlin and Al Milgrom, Thanos not only restores the heroes that long bedeviled him but ends up saving the entire Marvel Universe twice.
WHAT IS MARVEL UNIVERSE: THE END?
Millions of years ago, alien explorers found the all-powerful Heart of the Universe, which granted them extreme power. Now known as the Celestial Order, they spread power across all of creation by giving pieces of it to "worthy" rulers. This included Akhenaten, a cruel and petty Pharoah from Ancient Egypt. With his newfound power, Akhenaten returned to the more modern Marvel Universe and tried to take over the world. Akhenaten demanded dominance over the planet from his city of Tell-el-Amarna and showcased his sheer power by casually curing disease across the planet.
Akhenaten then deals with threats to his rule: he casually destroyed the Shi'ar Armada and wiped out the X-Men with a massive fireball after Xavier and Jean Grey confronted him psychically to learn his intentions. He captured all of Marvel's time-travelers in an attempt to keep them from attacking his past - including Doctor Doom, who came the closest to success. He wipes out the Avengers and Fantastic Four just as easily as he destroyed the X-Men, and even hangs their bodies in crosses across New York City as a warning to other would-be rebels.
Only a handful of heroes who weren't present survive these attacks, and many of the surviving ones -- like Daredevil, Spider-Man, Black Widow, Hawkeye, and Black Cat -- are hunted down by Akhenaten's new Imperial Police, which is composed of powerful villains like the Wrecking Crew and Absorbing Man. Meanwhile, the Defenders -- Hulk, Doctor Strange, Namor, Silver Surfer and Genis-Vell's Captain Marvel -- are approached by Thanos, who offers his assistance while they search for more knowledge about how Akhenaten became so powerful.
During their search, the Pantheons observe Akhenaten but are almost all wiped out by him. However, both Thor and Zeus are saved by Eternity. Meanwhile, Thanos and the Defenders find the Heart of the Universe. Thanos absorbs the infinite power of the Heart into his body at the cost of the Defenders' lives. Thanos confronts Akhenaten in the moment he prevented Doctor Doom's attack, and they engage in a duel with equal omnipotence. Thanos defeats Akhenaten and allows Doom to kill the younger Akhenaten to change the time-stream. Then, as an extra precaution, Thanos used his divine power to make sure the Celestial Order never found the Heart of the Universe in the first place. This restored the Marvel Universe and resurrected all the heroes, with only Thor and the other Celestial Powers remembering the truth.
HOW DID THANOS SAVE THE MARVEL UNIVERSE?
While Thanos broadens his perspective across all of creation and finds a fatal flaw in the construct of the universe that will soon destroy everything, Thor's army of heroes confronts the omnipotent Mad Titan. After a short battle, Thanos used his powers to absorb every one of his opponents and then everything in the universe - leaving nothing in the cosmos to threaten him and his eternal rule. To Thanos' surprise, there was only one survivor: his old adversary Adam Warlock. He had been outside of reality during this entire ordeal, so Warlock survived the end of reality.
Warlock speaks with Thanos for a period of time and convinces him to restore everything to as it was before Akhenaten arrived, even though the act would kill him. Lady Death appears before Thanos and kisses him in thanks for his sacrifice to restore everything. Only Adam Warlock is allowed to remember Thanos and his sacrifice, and he commemorates the loss of the Mad Titan on the quiet farm world that Thanos had visited multiple times over the years.
While there was some mild uncertainty about whether or not this story was Marvel Universe canon or not, it's surprising to find at least one reality where Thanos really did some selfless good and helped actually save the day. This makes this Thanos perhaps one of the only The End stories with a happy ending, as he made peace with the universe and even found Death's genuine affection - even for just a moment.