The Infinity Gauntlet is a cosmic artifact that grants the wearer complete mastery over the Infinity Gems.
Mistress Death resurrected Thanos to correct an imbalance in the fabric of the universe in the realization that there are more people alive than had ever died. She brought him back from the dead and gave him the gauntlet with the agreement that he do something about all the living in the present day. Thanos spent time at the Infinity Well; the supposed source of all universal knowledge. In his research he discovered the true nature of the Infinity Gems. He then sought out the gems from the unwary owners (The In-Betweener and Elders of the Universe). He assembled the six infinity gems on his own golden glove creating what becomes known as the Infinity Gauntlet.
Thanos then spent time practicing with the gems. He kept his promise to Mistress Death by eliminating 50% of the universe's population. All of Earth's mightiest superheroes that remained went after Thanos to stop him. But they needed someone who knew Thanos like no one else does, better than Thanos himself. Adam Warlock stepped in to help Earth and it's heroes. Thanos lost the gauntlet to Nebula, and she subsequently lost it to Warlock. He took the Gauntlet and became a god. In order to make himself a noble god he subconsciously expelled all good and evil from his body creating the Magus and the Goddess. Shortly afterwards he gained the power of the Gauntlet. The Living Tribunal appeared and forced Warlock to give up his power, and Eternity declared that the gems could never be used together again.
The gems were split up among Warlock and his closest companions, Moondragon, Drax, Pip, Gamora, and secretly giving the last one to Thanos. This group minus Thanos became the Infinity Watch.
During Infinity War the Magus traveled across dimensions and collected 5 cosmic cubes. He planned to make a machine that could help him acquire the Infinity Gauntlet that would be free from the Living Tribunal's decree that the gems would no longer work in unison. Magus forced Eternity into a coma like state and created warped doppelgangers of every hero on Earth with the clone of Thanos working as his right hand man.
Earth's mightiest heroes were forced to team-up with Thanos and Galactus to stop Magus. Warlock took back all the gems and tried to use the Gauntlet with little success. They realized that the ruling from Eternity was still in affect. Galactus traveled to speak with Eternity and the Living Tribunal to have the ruling on the use of the Gauntlet reversed. However, Eternity was the only entity that could reverse the decree, but he was still in a coma. Galactus set about restoring him with the help of Gamora. Meanwhile, Magus kidnapped Warlock, stealing the Infinity Gauntlet and held them prisoner in his citadel. Eternity was brought out of his coma long enough to reverse his ruling, and the Gauntlet became functional once more.
Magus began adjusting to his new power and unleashed all of his doppelgangers against Earth's heroes. Magus then froze everyone and teleported them into his citadel to become his trophies, but he was ambushed by Thanos who had been fighting his own doppelganger in another part of the citadel. Warlock broke free of his restraints and grabbed onto the Gauntlet. Because of his greater knowledge of how to use the Gauntlet, and the fact that the Reality Gem which Warlock inserted in the gauntlet was a fake, he was able to overpower Magus and absorb him back into his body. Eternity and Infinity appeared saying that no matter what the circumstances the gems would never work in unison ever again. The gems were divided up once again among the Infinity Watch.
Reed Richards calls the group together and reveals to them that he has been gathering the infinity gems with the Gauntlet and three of the gems already in his possession. After they manage to gather the remaining gems, The Watcher, appears before them and warns Reed that the power the gauntlet contains is too much for one man to wield on his own. After some convincing Reed gives up the gems which are then divided up between the group and with the help of The Watcher are hidden far away from where anyone else may find them
During New Avengers, the Illuminati assembled the Infinity Gauntlet to prevent a Universal Incursion from destroying the two universes that were colliding with each other. Captain America wore the gauntlet and pushed the other Earth away from the Earth-616. Due to the immense amount of power required, their was a side-effect, which destroyed 5 of the 6 Infinity Gems and caused the Time Gem to disappear.
The Gems & Their Powers
Time Gem: Total control over all aspects of time including time travel, stopping time, slowing down or speed up flow of time and to accelerate or slow down aging.
Space Gem: Limitless manipulation of space, allowing for teleportation, dimensional manipulation, creation of wormholes, etc.
Soul Gem: Limitless manipulation of souls both alive and dead, also has shown to be able to evolve or devolve a beings physical self as well as their mental capacities.
Reality Gem: Locally or universally alters the natural laws of the universe to the wielders will.
Power Gem: Controls all of the power in the universe. It can be used to augment or inhibit any force.
Mind Gem: Taps the user into the universal consciousness, allowing for unlimited manipulation of psionic powers including telepathy and telekinesis.
Limitations: The Infinity Gauntlet only works in the universe it is from (why Darkseid pictured below could do nothing with it). Since the end of the Infinity War, Eternity states that "Let it be known the power that the Living Tribunal represents will never again allow the gems to work in unison. No matter what the crisis." effectively stating that the gems will never be able to work together ever again.
Powers & Abilities
The Infinity Gauntlet itself has no power, it is merely a device to contain all the gems in one location. Anyone with the knowledge of the whereabouts of the gems can obtain the Gauntlet, but it takes much more than holding the Gauntlet to wield it's power. Like the gems themselves, it takes much knowledge and discipline to accurately use the infinite power of the Gauntlet and become a God.
Ultimately, the power of the Infinity Gauntlet is not meant for mortals, as mortals are not meant to be gods. This is evident in conversations between Thanos and Adam Warlock, both having achieved and lost their godhood. Both had voluntarily given up their power, realizing that it was not theirs to have. After giving up their power, the knowledge and godliness they had slowly melted away, being a haunting reminder of the immense power and responsibility they once had.
Those who have wielded the Infinity Gauntlet:
In the Ultimate Marvel universe, the Infinity Gems actually combine to form two separate Gauntlets. They are assembled by the various members of the Ultimates before being stolen by Reed Richards and his team of Dark Ultimates, with the Hulk initially donning them to battle his former teammates. The Gauntlets and Gems are later shattered, and the Dark Ultimates are defeated.
The Super Hero Squad Show
The Infinity Gauntlet appears in the second season of The Super Hero Squad Show, with a major running plot involving Thanos trying to find the various Infinity Gems. In the finale, he forms the Gauntlet and uses it to battle the heroes, only to have it stolen by the Dark Surfer. The Surfer combines the Gauntlet with the power of the Infinity Sword before both items are shattered, creating the Infinity Fractals.
The Infinity Gauntlet appears in the second season of Avengers Assemble. In the episode "Widow's Run", Thanos forms the Infinity Gauntlet after stealing the remaining Infinity Stones from Black Widow.
The Infinity Gauntlet makes a brief, split-second cameo in Thor, where it can be seen in Odin's treasure room. The various Infinity Gems have since appeared independent of the Gauntlet (in Captain America, The Avengers, and Guardians of the Galaxy), implying that the one seen in the treasure room may be a replica, or alternatively simply does not possess any powers.
Avengers: Infinity War: Part 1 and 2
The Infinity Gauntlet will appear in the two-part film Avengers: Infinity War, presumably as the main focus. The teaser trailer for the film shows Thanos wielding the Gauntlet just before the screen fades to white.