The Mind Gem gives it's user amplified psychic and psionic abilities. With an already psychic user, these abilities are nearly limitless. Powers include telepathy, empathy and telekinesis. The Mind Gem can access and alter thoughts and dreams, create or remove mental barriers and blocks, influence actions, alter or create memories and feelings, and perform impressive feats of telekinesis and psychokinesis.
With the other gems, these powers are amplified even further to which all minds in the known universe can be accessed simultaneously.
The Mind Gem, along with the other Infinity Gems, were gathered by the Elders of the Universe in a plan to destroy Galactus. After their defeat, the Mind Gem went into the custody of the Grandmaster. When Thanos begins to gather the gems, he plays a game of wits with the Grandmaster for the gem. Although the Grandmaster cheats, so does Thanos, who gains custody of all the gems and controls the Infinity Gauntlet, thus becoming a god.
After Thanos's defeat, the Gauntlet briefly goes into the custody of Adam Warlock, who soon gives the gems to the protection of his choosing - thus creating the Infinity Watch. Moondragon, already a powerful telepath, is given custody of the Mind Gem.
After briefly being taken by the Magus, the Infinity Watch is eventually disbanded and the gems are spread across the universe. The gems were gathered by the Illuminati and the Mind Gem given to the custody of Professor X.
When a young Odin was in search of conquests he defeated Hidelbard, smartest giant in Jotunheimr. In doing so he gained his intelligence which proved to be overwhelming to Odin. The Nine Realms condensed the power into a single gem which became the Mind Gem.
During Divided We Fall, Thor's son Modi, took possession of the gem and used it to control Thor and have him fight against the Ultimates.
Wielders of the Mind Gem