Thanos was one of the last sons of A’Lars, progenitor of the second colony of Eternals on Titan, and Sui-San, the last survivor of the original settlement of Eternals on Titan. Born with grey, hide-like skin and a massive body due to being born with the Deviant Syndrome, Thanos was a morose child who became obsessed with the concept of death.
Through bionic implementation and long hours of meditation, Thanos augmented his Eternal strength and powers so that his powers surpassed those of all other Titanian Eternals. As he grew in power, Thanos also grew in ambition and desire for conquest. Thanos stole one of his people’s starships and traveled to other star systems to recruit soldiers, mercenaries, and malcontents for a private army. With a small fleet, he dropped nuclear devices on his home world Titan, killing thousands of his people, including his mother Sui-San. Declaring himself ruler of Titan, he then set his sights on Earth.
At some point in his adult life, Thanos met the embodiment of Death itself who, in female form, became Thanos’ companion. It is probable that Death was attracted to Thanos by both his philosophical dedication to nihilism as well as his willingness to commit genocide on even his own people. Thanos began, for the first time in his life, to experience love for another being, although the being was just a manifestation of Death. To make himself worthy of so awesome an entity, Thanos decided to acquire more power. At first he planned simply to seize political power through the conquest of worlds. To this end, he amassed a huge armada of battleships. Then he found a way to amplify immeasurably his personal power. Having kept the planet Earth under surveillance since it first exploded a nuclear weapon, Thanos learned of a power-object called the Cosmic Cube brought into existence by the subversive organization, Advanced Idea Mechanics. Thanos seized control of the reality-altering device and commanded it to give him control over the universe.
Transformed into a godlike wraith by the Cosmic Cube, Thanos battled the Avengers and the Kree Captain Marvel, the former of whom had already vanquished his armada. When Thanos carelessly discarded the Cube, believing falsely that he had drained it of all power, Mar-Vell struck the cube, willing it to restore the universe to what it had been. Robbed of power, Thanos reverted to mortal form in the center of the universe where his flagship Sanctuary II retrieved him under pre-programmed instructions. Revived, Thanos was dejected to discover that Death had abandoned him because of his failure. He soon formulated a plan to regain “her” affection: he would give to “her” more than any single living being had given “her,” the annihilation of everything that lives. Through the minds and records of countless civilizations he searched, hoping to find the key to the power he sought. Eventually he learned of the Infinity Gems, six power objects of unknown origin and vast power, and set about to acquire them. He had obtained all of the Infinity Gems except one, the jade jewel worn on the head of Adam Warlock.
Thanos feared to acquire Warlock’s gem directly because it possessed the power to steal souls, and he feared to risk forfeiting his own. Observing him, Thanos learned that Warlock had diverged a temporal counterpart named the Magus, who was the head of a galaxy wide religious empire and would certainly oppose Thanos’ schemes of stellar destruction were he to learn of them. Thanos thus planned to eliminate the Magus. Possessing the capacity for time travel, Thanos decided to set up certain factors in the time stream which, combined, might prove the Magus’ undoing. (He could have tried to thwart Warlock’s life well before the critical time he would/wouldn’t become the Magus, but he needed Warlock to remain the Soul Gem’s possessor for simplicity’s sake). One of these factors was the rescuing of the infant Gamora, a female of the pacifistic Zen-Whoberis race that was slaughtered by the Magus’ missionary troops. She would serve as Thanos’ personal assassin. The second major factor would be Thanos’ own direct alliance with Warlock against the Magus. Neither of these factors existed in the original time-line that led to the Magus’ creation; thus, Thanos hoped to diverge a reality wherein Warlock never became the Magus. Thanos succeeded, and while in close proximity to Warlock, siphoned from his Soul Gem the energies he needed without Warlock’s knowledge.
Thanos then constructed a single huge synthetic Soul Gem to hold the energies of the other six. With it, he planned to extinguish the stars one by one. Gamora learned of his plan of destruction and tried to assassinate him, but Thanos slew her. Thanos also slew Warlock’s comrade Pip the Troll. Warlock had by this time learned of Thanos’ threat and traveled to Earth to enlist the aid of the Avengers and Captain Marvel. In battle aboard Thanos’ starship Sanctuary II, Captain Marvell damaged Thanos’ projector through which he transmitted the synthetic Soul Gem’s energies into suns to cause them to go nova. Warlock faced Thanos in personal combat and was slain. The Avengers were taken captive by Thanos, but rescued by Spider-Man and the Thing. Spider-Man, influenced by the abstract entities Lord Chaos and Master Order, released Warlock’s spirit from the Soul Gem Warlock had worn, and seething with cosmic power released through his physical death, Warlock grappled with Thanos and turned the mad Titan to immobile stone. Incapacitated, Thanos retained a fragment of his consciousness and was thus tortured by the fact that he who worshiped death would forever be denied it.