The Mind Gem gives its user amplified psychic and psionic abilities. With an already psychic user, these abilities are nearly limitless. 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' 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 young Odin was in search of conquests, he defeated Hidelbard, the 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. After his death, the Gem was taken and later incorporated into the Infinity Gauntlets.
Wielders of the Mind Gem
Marvel Cinematic Universe
In The Avengers, Loki wields a glowing blue staff given to him by the Other. The staff is not explicitly identified as the Mind Stone until later films but is shown to be a cosmic artifact capable of controlling the minds of others. Loki uses it to brainwash Hawkeye, Erik Selvig, and several others, before Black Widow is able to wield it to shut off the Tesseract.
Captain America: The Winter Soldier
In the mid-credits scene of Captain America: The Winter Soldier, the Scepter is shown being studied by Baron von Strucker in a HYDRA facility. The prequel comic This Sceptre'd Isle later reveals that HYDRA first came into possession of the Scepter after one of their double agents within S.H.I.E.L.D. killed the scientist examining it. The Scepter was used to grant powers to Wanda and Pietro Maximoff, who were the only humans able to withstand its cosmic energy.
The Avengers: Age of Ultron and Captain America: Civil War
The Scepter reappears in Avengers: Age of Ultron. At the start of the movie, the Scepter is reclaimed by Iron Man, who uses it to help create Ultron. Ultron later destroys the Scepter, revealing the Mind Stone inside. He then forces Helen Cho to place the Stone inside a synthetic body, which results in the creation of the Vision. At the close of the film, Thor entrusts Vision with the Mind Stone, claiming that the android has proven himself worthy. Vision continues to use it through his next appearance in Captain America: Civil War.
Avengers: Infinity War
Thanos and his generals make it to Earth to steal the Time and Mind Stones. They attack Vision, who is able to get away after Captain America's outlaws intervene. They team up with the remaining official Avengers to bring Vision to Wakanda, hoping Shuri would be able to separate Vision from the stone. However, they fail, and Thanos pulls the stone from Vision's head, killing him in the process.
After Thanos successfully collected the stones and wiped out 50% of all life, he used the power of the stones to destroy the stones so that no one could take them and undo his work Five years after that, Tony Stark figures out time travel based on Hank Pym's tech and Scott Lang's observations. Captain America travels back to the Battle of New York to steal the scepter from Hydra goons (posing as SHIELD) and bring it to the present with the other stones.
After undoing Thanos' actions, Captain America would return all the stones from when they were taken.