Palkia, known as the Spatial Pokémon, is a legendary Pokémon and part of the Legendary Dragon trio, along with Dialga and Giratina. It represents spatial matter whereas Dialga represents time and Giratina represents dimension. Palkia, like Dialga, has a dinosaur-like appearance, but is more similar to a theropod, contrast to Dialga being similar to a sauropod. Palkia has wings on its back which can open up and purple stripes on its neck and tail. Palkia also has a pink pearl on each shoulder plate. In Sinnoh-region lore, it and Dialga are said to be created by Arceus, at which point time and space began to take form and matter began to take shape. According to Platinum, Palkia's breath keeps space and matter stabilized. Its signature move is "Spacial Rend", a powerful blast of energy that can distort space, much like Dialga's "Roar of Time" and Giratina's "Shadow Force", which influence their respective elements.

Palkia is not obtainable in Diamond, in the same way that Dialga is not obtainable in Pearl. In Pearl, it is summoned by the defeated leader of Team Galactic, Cyrus, who hopes to have it create a new universe for him, at the Spear Pillar on top of Mt. Coronet. It is stopped by Uxie, Mesprit, and Azelf, which nullify its power, and can be captured or defeated by the player. In Platinum it can be caught after finding the Lustrous Orb and returning to the Spear Pillar. Palkia is faster than Dialga and Giratina but has slightly weaker defensive stats. Its special item is the Lustrous Orb, which amplifies Palkia's Water- and Dragon-type attacks when held by it.

Palkia also appears in the Wii title Super Smash Bros. Brawl in the background of the Spear Pillar stage, along with Dialga and Cresselia. Like Dialga, Palkia will occasionally attack the players or sometimes the stage itself. Palkia makes an appearance in tenth movie of the Pokémon anime along with Dialga and Darkrai, in which it fights with Dialga and nearly destroys Alamos Town. In Pokémon: Giratina and the Sky Warrior, it did not have a main role, but appeared in a flashback to its battle with Dialga from the previous movie. Finally, in the twelfth movie, Palkia, alongside Dialga and Giratina, attempts to stop their creator while Ash and friends travel back in time to fix the past.

In an interview, Pokémon Diamond and Pearl director Junichi Masuda noted Dialga's and Palkia's name as two of the most difficult to create, due to an effort to make them appealing to both Japanese and American audiences.