The Mad Titan Thanos is infamous throughout the Marvel Universe not only for his brute strength but also for his cunning and brilliance which has helped defeat Marvel's greatest heroes a plethora of times. His most famous defeat of the heroes came in Jim Starlin, George Perez, and Ron Lim's "Infinity Gauntlet" event, the culmination of his quest to gather all six Infinity Gems, which later inspired the first three phases of the Marvel Cinematic Universe.
Inversely, in Marvel's Ultimate Universe, or Earth-1610, the Mad Titan of this universe has little interest in the Infinity Gems and his sights set on the ultra-powerful Cosmic Cubes.
In the main Marvel Universe of Earth-616, Thanos embarks on his "Infinity Quest" to collect the six Infinity Gems to impress Mistress Death, his unrequited love interest. However, despite collecting all six and killing half of all life in the universe, Mistress Death rejects Thanos, completely breaking him. Contrarily, the Ultimate Marvel Thanos, who made his debut in Mike Carey and Pasqual Ferry's Ultimate Fantastic Four #35, disregards the Gems and his quest to earn the love of Mistress Death in favor of the Cosmic Cubes and becoming the sole ruler of the entire universe.
It is revealed that in the Ultimate Universe, some 13,000 years ago, the Cosmic Cube landed on the planet Acheron and was discovered by a young Thanos. Thanos wielded the Cube's power to fuel his conquest of the universe and impose his will upon those who opposed him and his order. However, the expansion of his order was stopped by Mother Induna of Halcyon who sacrificed her life to bring his conquest to an end. Despite the end of his expansion Thanos still ruled his empire with an iron fist, brutally suppressing any resistance to his rule. Discovering Reed Richards and recognizing his ability to construct a Cosmic Cube, Thanos possesses Ben Grimm to meet with him, requesting Reed to construct a new Cosmic Cube or see Thanos kill Johnny Storm. Ultimately Ben manages to resist Thanos and Reed declines to construct a Cosmic Cube for Thanos but does construct one to use against him.
Thanos reemerges in Mike Carey and Pasqual Ferry's Ultimate Fantastic Four #50-53, obtaining Reed's Cosmic Cube and using it to conquer Earth, brainwashing Earth's heroes into fighting his enemies for him in the process. In Carey and Ferry's Ultimate Fantastic Four #53, Thanos uses Reed's Cube to finally attempt ascending to Godhood but immediately realizes something is wrong and is destroyed by the Cube.
Reed reveals that he had built a cut-out into the Cube but removed that cut-out while Thanos was distracted, causing the Cube to kill its user. Reed finally disposes of the cube into a time-rift, depositing the Cube on Acheron 13,000 years in the past where Thanos initially found it, thus creating a paradox that the events of the future led to the events in the past and vice-versa.