Team Galactic is the crime syndicate in the Sinnoh region, which is the setting of the video games Pokémon Diamond and Pearl. The team’s commanders (Mars, Jupiter, and Saturn) are named after planets.
In Diamond and Pearl, Team Galactic state their intention to create a new world order. However, only Cyrus and his commanders know the true details (and even then, Saturn is not entirely clear on this)--that this will first entail the total destruction of the current world to allow the presence of the new. They kidnap the legendary Lake Trio (Uxie, Mesprit, and Azelf) and extract crystals from them to create an item known as the Red Chain, which shackles and controls a Pokémon, yet keeps their full power (according to Cyrus' files, they do not plan to keep their target in a Poké Ball, in which they claim that it will restrain its full power). The player infiltrates Galactic's headquarters and defeats Cyrus, so he allows the player to release the three after beating Saturn. At the Spear Pillar, Cyrus uses the Red Chain to bring the legendary Pokémon Dialga (in Diamond) or Palkia (in Pearl) out, planning to use their power to distort spacetime and so create the new universe, over which he will be the new deity (or so he thinks). However, the Lake Trio come back to nullify the legendary's power and break the Red Chain, interrupting the ritual. After this, and Cyrus's failure to defeat the player, most of Team Galactic disappears including Cyrus himself. Only a handful remain in Veilstone City, led by Saturn, who has renounced his earlier extremism and decided to found a new, more benevolent Team Galactic.
In Pokémon Platinum however, Team Galactic plans to captivate both deities of time and space, resulting in the interruption of an enraged Giratina, the third Sinnoh deity who represents dimensions, chaos, and death. The player will have to chase down Cyrus, now infatuated with the power of the before-unknown Giratina, to an eerie dimension known as the Distortion World (Yaburareta Sekai), in which Giratina has resided for countless ages. Later in the game, it is revealed that Mars and Jupiter quit Team Galactic. It also features a new Team Galactic member named Charon, who is arrested shortly after Mars and Jupiter quit.