Groudon is a giant, stylized theropod with a layer of outer skin composed of a warm red, rocky substance and a stylized sloped tail with "tines" on the end like a rake; Groudon's tail is curved upward, making Groudon's contour look somewhat like an "S" shape. However, it can also stand in a more upright position. Groudon has narrow ridges on its head, long white claws, sharp teeth, and a grey chest. When angered, its black markings glow blue. Groudon resembles Godzilla in some respects as well, especially his fake clone in the Jirachi movie.

The heaviest of all Pokémon, Groudon represents the primal force of the land, as opposed to Kyogre (the primal force of the oceans) and Rayquaza (the primal force of the sky); as such, Groudon has the power to scatter rain clouds and make water evaporate with light and heat. It is literally "the land lord", as it is part of the creation myth of the Pokémon world. According to legend, it came as a savior to people who had been suffering from terrible floods by waging a titanic battle with Kyogre, creating the land and the oceans, and the two were sealed beneath their respective elements.

Groudon and Kyogre have a relationship similar to the Behemoth and Leviathan in Jewish mythology. In Jewish mythology, Behemoth is the primal unconquerable monster of the land, just as Leviathan is the primal unstoppable monster of the oceans. Rayquaza is also based on Ziz, another creature of Jewish mythology, as according to one Jewish myth the meat of the three creatures is to be served at the banquet at the End Times. Their appearances, however, are quite different from the traditional depictions of the creatures from Jewish myth: Groudon is a sloped, heavily-built dinosaur-like biped with a particularly powerful tail, while the Behemoth is often portrayed as a massive ox-like creature.

Team Magma seeks to capture Groudon and expand the land, while their rivals, Team Aqua, seek to awaken Kyogre and expand the oceans. In the episodes "Gaining Groudon" and "The Scuffle of Legends", this conflict climaxes when the orbs that control Kyogre and Groudon fall in the hands of their respective Teams, and the two Pokémon are made to wage a battle against each other. At the end of the second episode, Team Aqua and Team Magma's opposing plans are foiled by Ash Ketchum and Lance, and Groudon and Kyogre return to their respective elements after calling a truce. It also appears as part of the legend in "The Spheal of Approval" and "Unfair Weather Friends".