Six Marvel superheroes that Thanos decided to be worthy foes capable of defeating him were made public when he obtained the Cosmic Cube. The Mad Titan utilises the potent cosmic relic to put six heroes into stasis in Captain Marvel #31 by Marvel Comics, where he then acknowledges that without them on the field, no one could stop him. Fortunately for the frozen heroes, they succeed in escaping Thanos' trap, but not before he displays his abilities.
In the Marvel Universe, Thanos is a force of unbridled power because he frequently uses the Infinity Stones to bend reality to his will. The six Infinity Stones were most famously utilised by Thanos to wipe out half of all life during the Infinity Gauntlet Saga, a battle that was dramatised for live-action in the Marvel Cinematic Universe. However, one of Thanos' first tasks after obtaining the Cosmic Cube was to eliminate six heroes he believed to be worthy foes who could prevent him from abusing the enormous powers of the artefact for his own benefit.
In one of Thanos' earliest tales, Captain Marvel and Moondragon team up with the Avengers and Drax the Destroyer in Captain Marvel #31 by Jim Starlin, Dan Green, Al Milgrom, and Tom Orzechowski of Marvel Comics to combat the impending menace of Thanos, who had obtained the Cosmic Cube. Thanos confesses that there are six heroes that are worthy of being stopped by him: Iron Man, Captain Marvel, Drax the Destroyer, Moondragon, Starfox, and his father, Mentor. However, with the cube, Thanos can see the onslaught coming.
The Six Heroes are Removed by Thanos for Very Specific Reasons
In a monologue, Thanos explains why he removed the six heroes from the game: Due to his cosmic understanding, Captain Marvel is too dangerous, Iron Man has already come close to stopping him twice and could do so again, Drax is more motivated than most heroes due to his desire to destroy Thanos, and Moondragon is a real threat due to her Titan ancestry. Starfox and Mentor are included in the group, and Thanos warns that their link to him and Titan powers make them dangerous. Thanos even acknowledges they are "worthy foes" who have "stood in his way," something he actually admires, as he imprisons the six heroes in a bioelectric field.
When the six heroes manage to escape his grip and engage him in a battle for the Cosmic Cube, it turns out that Thanos was right to worry that they were his most worthy adversaries. The deserving heroes would finally discover a method to stop the Mad Titan, even if triumph appeared to be inevitable. The six characters demonstrated that Thanos was correct to try to stop them with the use of his abilities and that they were the biggest obstacle to his Cosmic Cube success.