The Infinity Gauntlet is a golden gauntlet that was designed to hold 6 of the "Soul Gems", better known as the Infinity Gems. When used in combination, their already impressive powers make the wearer able to do anything he/she wants (though it has been revealed that alterations to time and space *only* work in a single universe, meaning that an Infinity Gauntlet from an alternate universe would have no power in "mainstream" Marvel and so on, furthermore the Infinity Gauntlet has no power whatsoever in universes outside of Marvel's Multiverse, since in Avengers/Justice League an Infinity Gauntlet manifested in the DC universe, yet was deemed "worthless" by Darkseid, who tossed it away).
It was gathered by the mad Titan Thanos as he took the gems from the Elders of the Universe that had originally carried them.
Adam Warlock later held the gauntlet, but the Living Tribunal declared that the gems were too dangerous to use together. However, Thanos' later machinations eventually led to the Living Tribunal rescinding this restriction.
Later in the future, Mr. Fantastic revealed to his fellow teammates of the secret group called the Illuminati that he had been collecting the Infinity Gems, and hoped to collect them all with the help of them. Despite a general apprehension, the group managed to acquire all six gems. Upon doing so, Mr. Fantastic attempted to will the Gems out of existence, but he was unable to do so. Faced with this failure, and a reprimand from Uatu, the Watcher, he made the controversial decision to give each Illuminati member one gem to hide so that they would never be combined and used again.
After the Siege of Asgard, The Hood tried to get all the Gems, starting by taking the Reality Gem from the Himalayas (which was kept there by Illuminati Black Bolt), the Power Gem from the Baxter Building (kept by Mr. Fantastic) and battled the Red Hulk with it. Red Hulk warned the Avengers about it, and Iron Man talked with the Illuminati about this. Hood managed to get the Space and Time Gems, while he lost the Power Gem at the hand of Red Hulk, Namor and Thor. After taking the Mind Gem from the ruins of the X-Mansion, Hood traveled to the Astral Plane, where he tried to get the Soul Gem, but was finally defeated by the Avengers. Iron Man gathered all the 6 gems and became the first human to possess and use the Infinity Gauntlet, as he transported the Hood back to Ryker's Island and faked that he made the Gauntlet disappear from existence, he really transported it to the Illuminati gathering place, where he divided the Gems between his teammates again.
When the Illuminati later confronted the threat of the Incursions, alternate reality Earths colliding with their own with the result of the extinction of both realities, the Illuminati once again assembled the Infinity Guantlet.
Galactus, The Watcher and Thanos sensed the assembly of the gauntlet, and Captain America used the Gauntlet to push away the other Earth and prevent the collision. The cost of this however, was the destruction of the Gauntlet and the shattering of all gems but the Time Gem.