Thanos's Kennel
Thanos, referred to as the Dark Lord by his most loyal underlings and the Mad Titan by the galactic community, is a powerful, extremist, genocidal, psychopath, violent and tyrannical Titan warlord who rules over a distant region of space and commands two massive armies, known as the Chitauri and the Outriders, and a small group of followers known as the Black Order. His own main objective was to bring stability to the universe, as he believed its massive population would inevitably use up the universe's entire supply of resources and condemn it. However, his methodology to succeed was warped; through using the Infinity Stones, Thanos intended to harness their power to exterminate half of all life in the universe.
He spent many years hunting down these stones and his desire to achieve this ultimate goal is what led Thanos to forge new alliances with Loki and Ronan the Accuser in their respective campaigns against Earth and Xandar,promising to aid them in exchange for an Infinity Stone. Both alliances cost Thanos much of his resources, including one of the stones and the loyalty of his adopted daughters, Gamora and Nebula, and inadvertently resulting in the formation of the Avengers and the Guardians of the Galaxy. Fed up with all his subordinates' failures, Thanos opted to seek out the location of the Infinity Stones himself.
Thanos engaged in a ferocious warpath in order to obtain all of the Infinity Stones. In his journey, both he and his Black Order invaded Nidavellir, Xandar, Earth, and Knowhere. During this, he murdered Loki, along with many Asgardians, and even his beloved Gamora in order to obtain the Soul Stone. The primary aggressors fighting against Thanos became an alliance comprising the Avengers, Masters of the Mystic Arts, Guardians of the Galaxy, and the nation of Wakanda. Despite facing off against a powerfully combined opposition and the wrath of Thor, Thanos ultimately triumphed over his enemies and completed the Infinity Gauntlet, using it to finally complete his goal and erase half of all life within the universe at the snap of his fingers.
Thanos was born to A'Lars, a member of the Titans, a race of powerful, god-like beings that evolved on a planet. Thanos unconditionally loved his people and desperately sought to save Titan when the planet became threatened by the imminent catastrophic event of overpopulation. When Thanos suggested killing half the population of the planet to solve the problem, his idea was considered too drastic and was dismissed by his people, which resulted in Titan becoming subsequently devastated as well as nearly uninhabitable. Another result of this devastation was that the Titan species was on the verge of extinction.
Sometime after Titan's fall, Thanos came to believe that the universe's large swell of life was depleting its finite resources, and would eventually cause the destruction of the universe itself. Hence, to save other planets from Titan's fate, Thanos became a world-conqueror, moving throughout the universe and destroying half of all life within the planets he conquered due to his ideology of balancing the universe. He earned such a fearful reputation as a galactic warlord, due to his immense power and even ruling over a distinct region of space, and gaining control over the deadly armies of the Chitauri and Outriders, that he was considered among the most powerful, if not the most powerful, being in the universe.
Sometime later, Thanos brokered a deal with his old ally, Ronan the Accuser of the Kree Empire, promising to lend a fraction of his forces in a genocide against the Xandarians in exchange for locating the Orb for the Mad Titan. Ronan and Korath the Pursuer quickly discovered the Orb on Morag and attempted to deliver it to Thanos, but the stone fell into the possession of a Ravager called Star-Lord who was trying to sell it to Broker before Ronan could claim it.
Unwilling to be denied the stone, Thanos ordered Ronan to pursue Quill and recover the stone, sending Gamora to aid the Kree in his pursuit. Gamora found Quill first, cornering him on Xandar where he was attempting to sell the Orb. She recovered it, but what Thanos did not realize is that Gamora had chosen to cut all ties with him, due to the torture she and her many siblings have suffered through from the Mad Titan and planned to hand the Orb over to the Collector, who also sought the Infinity Stones for his own purposes.
When Ronan relayed news of Gamora's betrayal to Thanos which he had learned had been planned for some time, the Kree berated the Mad Titan for not taking the situation seriously and even murdered The Other when he lectured Ronan on not showing Thanos respect. Undaunted by The Other's death and Ronan's complaints, Thanos turned Ronan away, instructing him to return to his task and correct Gamora's betrayal, which he was only slightly irked by. Thanos then instructed Nebula to take Gamora's place as Ronan's aide.
With both Loki and Ronan the Accuser having failed Thanos in their tasks of conquering worlds and bringing him the Infinity Stones, and both of his daughters lost to him, Thanos, fed up with the failures, had finally grown tired of the lack of progress in his crusade and decided to take matters into his own hands. He forced the dwarves of Nidavellir to forge the Infinity Gauntlet in order to control the power of all the six Infinity Stones at once before massacring them all, leaving only the Dwarf King Eitri alive, whose hands he cut off. Thanos then began to hunt for the Stones himself, believing himself to be capable of completing the task while smiling confidently to himself at the prospect of victory.
The Confederacy, an intergalactic alien alliance, learned about Thanos' intentions. When HYDRA managed to communicate with the Confederacy, they warned them about the Mad Titan and the threat he posed to humanity, so they offered their service to protect Earth. However, they knew they were no mach against the forces of Thanos, so they only exploited the deal in order to get from HYDRA Earth's resources, primarily Inhumans and Gravitonium.