Thanos is one of the most feared villains in the Marvel Universe, and he's usually one of the few villains who can truly accomplish his dark goals. In the Marvel Cinematic Universe, the Mad Titan successfully wiped out half of all living beings in the entire galaxy with the all-powerful Infinity Gauntlet before his showdowns with Earth's Mightiest Heroes in Avengers: Endgame.
As scary as Thanos is, he almost went by a drastically different name. While it may seem unlikely, the backstory on what Thanos' mother originally planned to name him was revealed in Thanos #13-18, by Donny Cates and Geoff Shaw. "Thanos Wins" tossed the Mad Titan into the far-flung future, where he met King Thanos, his future counterpart who finally succeeded in vanquishing all of Marvel's premier heroes and conquering the universe.
King Thanos sent his Black Right Hand, the Cosmic Ghost Rider, to retrieve Thanos from the present-day using a shard of the Time Stone. Every murderous act committed by King Thanos was driven by the need to win the affection of Lady Death. However, the millennia and eons proved that Lady Death was still waiting for King Thanos to deliver one more slaughter in her name.
The older Titan led the younger Thanos to believe he was brought to the future so they could team up to defeat the Fallen One. Only then would Lady Death give herself up to the king. The identity of the Fallen One was revealed to be Norrin Radd, also known as the Silver Surfer and former herald to Galactus. The Silver Surfer brought the Annihilation Wave with him to face Thanos, King Thanos and the Cosmic Ghost Rider in what turned into an epic clash of the Mad Titans.
The first victim of the battle was the Cosmic Ghost Rider, who turned out to be the street vigilante, Punisher. Frank Castle died when Thanos invaded the Earth and slaughtered its heroes, but a deal with the devil Mephisto turned Castle into the latest Spirit of Vengeance. Unfortunately, with all life on Earth terminated, there weren't any souls left on the planet for him to torture. Thus, when Galactus came to Earth looking for alliances in his fight with King Thanos, Castle struck up a deal to become the villain's newest herald. That partnership didn't last long, however, and once King Thanos killed Galactus, Castle switched sides again to become King Thanos' Black Right Hand.
During King Thanos' rampage through the cosmos, he was even able to conquer the powerful Celestials, turning their bones into a temple fit for a king. This is where Cosmic Ghost Rider brought the present-day Thanos after his time-travel kidnapping. Once Thanos laid eyes on his older, gray-haired counterpart, he predictably reacted with the only thing that comes naturally to him: extreme violence. When King Thanos dared to utter the word "please" in front of Thanos, it enraged the younger Titan. According to Thanos, a ruler of his caliber should never beg for anything. At the peak of their battle, King Thanos calls Thanos by his intended birth name: Dione.
The story of how Thanos earned his name begins on the planet Titan. Thanos was born to A'Lars and Sui-San, members of a race of aliens called Eternals. When Thanos' mother first laid eyes on him, she was driven insane and spit his name out without giving it an extra thought. While we now know this isn't the name she intended to call the Mad Titan, the story goes that Sui-San had never heard of the name before speaking it. So how exactly it came to her mind will go down as an intriguing unsolved mystery.
Thanos wound up killing his mother when he was 12-years-old, but before Sui-San passed, she spoke the name Dione to her son. That may have prompted Thanos to ruthlessly kill his own mother, or Dione may have simply been the last word she said aloud before the life left her body.
This revelation by King Thanos was enough proof for the younger Thanos that he was who he claimed to be. They finally put their differences aside and worked together for their shared goal, though they ultimately squared off in the finale of the "Thanos Wins" story arc. With all of the twists and surprises introduced, one that shouldn't be overlooked is what Thanos' name would have been if he wasn't born a Deviant. Regardless of that, his intended name -- or what it means to him at least -- may have played a meaningful role in pushing him towards his dark goals time and again.