Thanos' Quest was a tie-in to The Infinity Gauntlet to gain the Infinity Gems, and once he has them, he constructs the Infinity Gauntlet, a glove with each gem affixed, giving him complete control over Space, Time, the Mind, the Soul, and oddly also Reality and Power (the first four weren't enough for those, I guess), so that he would be a suitable consort of Marvel's Death. Well, Adam Warlock, who had been in charge of the realm inside the Soul Gem, isn't happy about Thanos having all this power, so he re-embodies himself and gathers the heroes of Earth together to take Thanos on. This may seem lopsided, but Adam also schemes to get many Cosmic Beings to help (Eternity, Love, Hate, Chaos, Order, even a Celestial or two, and others). Even with all that aid, the heroes fail.
BUT, Thanos loses the Infinity Gauntlet. It falls into the hand of Nebula, who claims to be Thanos' granddaughter. The heroes regroup, count the casaulties, and decide that they'll need all the help they can get. But Thanos, having once been omnipotent, is feeling a little bit sorry for himself, which he translates into scorn towards anyone around him (oh, Thanos, you so emotionally crippled). Adam, who has been completely composed and stoic throughout almost the whole of the rest of The Infinity Gauntlet, is not havin' any of that shit.
. . . dayum, son.
Later, Thanos gets the better of Adam, in a way, but first the heroes (and Thanos) launch their final assault against Nebula, and though Nebs is omnipotent, she is, shall we say, not omniscient. Or, not capable of utilizing her omniscience. Eventually, she loses the Infinity Gauntlet, and there's a mad scramble to retrieve it, but it was a forgone conclusion at that point. You see, earlier, Adam had contrived to get his ass zapped back into the world inside the Soul Gem, where his power is exponentially increased. Using that power, and his own will, he manages to take control of each of the other gems . . . from the inside.
And then this happens:
Eventually, the Infinity Gauntlet gets overused and destroyed and it's not worth getting into. But this was epic, is epic, and will always be epic.
And this series is also why I was so excited when Adam turned up during Annihilation: Conquest.