Dialga is a dark-blue, sauropod-like Pokémon with some gray metallic portions and light blue stripes. It has a chest plate on its torso, which has a deep blue diamond-like crystal embedded in the center. Dialga has a fin-like structure on its back, three spines on the back of its neck, and a crest on its head, resembling a dinosaur. It also has two structures on the sides of its head that extend outward and resemble horns and fangs. It has three claws on each foot, of the same metallic look as its chest plate. Faint cracks exist across its body. The fin-like structure on its back can be used to focus the flow of time, as seen in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness and Pokémon Mystery Dungeon: Explorers of Sky. Rather than walking on all fours, Dialga usually travels by levitation.
Dialga has the power to control time; it can warp time by either speeding it up, slowing it down, reversing it, or stopping it altogether; it can also travel through time to visit the past, present, and future. It also has the power to destroy and create time itself. As shown in the anime, Dialga's temporal powers possess the ability to devolve anything or anyone against their will: Pokémon, humans, and plants. It can even reverse these devolution effects. It is said that time started moving when Dialga was born and will continue flowing as long as Dialga's heart beats.
Dialga has the power to create a new universe by itself or with Palkia. As Dialga primarily resides in a different dimension, its behavior is nearly impossible to study. In the dimension where Origin Forme Dialga lives in, time is said to be constantly moving in different directions and speeds. It has been shown to be very protective of its home. It also tends to have violent conflicts with its counterpart Palkia.
Dialga is the only known Pokémon capable of learning the move Roar of Time, which is powerful enough to distort time itself when the move generates enough power.
Dialga can change between its standard form and its Origin Forme.
Said to be the Pokémon's true form, Dialga's Origin Forme is drastically different from the usual sauropod-like look of its other forme, being a hybrid between it, a dragon, and a centaur, while also resembling its creator, Arceus. The back legs of Dialga become unguligrade in shape and have pointed tips instead of feet. The front legs are noticeably larger, with three distinct rhomboid claws on the underside. Further up, Dialga's knees have rectangular, long, and thin protrusions. Its chest plate is gone; however, it has a similar polygonal shape in its place. On Dialga's neck is a large shape jutting out towards the front, along with two pairs of protrusions on either side, the upper pair being larger and resembling panels or wings. Inside this large shape and wing-like protrusions are deep blue diamond-like crystals, embedded into diamond-shaped grooves. The three spines located on the back of the neck are longer and sharper. Dialga's head has two thin arrow-shaped horns extending towards the top and back of its head, along with longer fang-like horns connected to a plate mask covering its lower jaw, which can shift in angle to reveal the mouth. The plate mask also partly covers the arrow-shaped horns on their sides. Around Dialga's abdomen is a cross comprised of four arrow shapes attached to a small wheel, reminiscent of Arceus's cross-wheel. The fin-like plate on Dialga's posterior has a star-shaped layer on top of it. The tail is much shorter and crystal-shaped. Overall, Dialga's entire body becomes larger and nearly completely dark blue. The crest, arrow-shaped horns, knee protrusions, and abdomen cross are light blue, while the tips of Dialga's fin-like plate and feet are dark gray.
Dialga is at its full power when in the Origin Forme and is supposedly, permanently in it while in its home dimension. Dialga's transformation into its Origin Forme is triggered by a radiant light; it can also be invoked using the Adamant Crystal. Origin Forme Dialga can unleash meteors and shockwaves, while its Roar of Time technique can be charged into a stronger version of itself as seen in its boss battle in Pokémon Legends: Arceus. The crystals and light blue accents on Dialga's body glow brightly when it uses its powers.
In The Battle Finale of Legend!, Dialga and Palkia were summoned by Cyrus on the Spear Pillar. They were put under his control through the use of the Red Chain and were tasked by him to open a portal to another dimension, wanting a world of his own. After the Red Chain's destruction and Cyrus's exit, Dialga and Palkia rampaged, creating a danger for Sinnoh. However, the two were calmed down and sent away with the help of the lake guardians.
In The New World, Dialga and Palkia were captured at Spear Pillar by Cyrus, who intended to use them to destroy the world and create a new one. Along with Palkia, it was freed by Giratina before they could help Cyrus succeed in his goal.
Dialga first appeared in Creeping Away from Cradily. Dialga, along with Palkia, was summoned by Cyrus in order to create a new world. Cyrus used the Red Chains to force Dialga and Palkia to fight each other in order to distort time and space and create a portal that would swallow the existing world. Diamond, Pearl and Platinum worked together with their Pokémon to free Dialga and Palkia from their controlled states.
Later on, an accident with handling Charon's machine caused Dialga, Palkia and Cyrus to be dragged into the portal before it closed completely.
It was revealed that Giratina imprisoned both Dialga and Palkia in the Distortion World before setting off into the current dimension to wreak havoc. Soon, Cyrus and Diamond met in the Distortion World, and agreed to free Dialga and Palkia using their Pokémon. Dialga and Palkia later resumed their struggle against Giratina in the Distortion World. When Charon decided to escape from the Distortion World on Giratina, Diamond got on Dialga and chased after him. Giratina was eventually defeated, with Dialga and Palkia forcing it back into the Distortion World for good before both returned to the Spear Pillar.
Dialga was created in the Sinjoh Ruins, along with Palkia and Giratina, by Arceus's creation process, which was forced by Team Rocket's Executives. Knowing that the creation process would threaten the Johto region, Team Rocket's true leader Giovanni returned with Lance and Pryce to keep the Pokémon of Myth at bay while Gold tried to calm Arceus down. Dialga was kept at bay by Pryce and his Swinub. Once Arceus was eventually becalmed, Dialga and Palkia departed from Johto and were spotted by Cynthia.
Dialga appears as a stage Pokémon along with Palkia, Cresselia, and the lake guardians on the stage Spear Pillar. It affects the stage much differently than that of its counterpart, such as slowing down time, and even going off its post to attack the players in the middle. It can also distort the stage, like Palkia, but only slightly and not as extreme, as well as shoot beams from various locations.
A Temporal Pokémon. This legendary Pokémon is talked about as a deity in fables passed down through generations in the Sinnoh region. Identifiable by the diamondlike crystal in the center of its chest, Dialga is said to have set time in motion at the moment of its birth. Its fearsome Roar of Time attack is so powerful that it must refrain from attacking on the next turn. It is Diamond's mascot.
The concept of time has always been one of the world's great mysteries, but Dialga might hold the answer. Legend has it that Dialga's birth caused time to begin moving! It's no surprise that the people of Sinnoh see this Pokémon as a deity. If you're ever running late, maybe you could ask Dialga to do you a favour and turn back the clock.
Dialga reprises its role as a stage hazard on the returning Spear Pillar stage. Spear Pillar now allows for any of the three Legendary Pokémon to appear each time, rather than being set for the whole match. Unlike in Brawl, Cresselia is now signified by the stage's color tint not changing from its new default green, rather than using Dialga's blue. Dialga also appears as a Spirit.
Pokémon Mystery Dungeon: Explorers of Time, Darkness& Sky: Dialga appears in the main storyline, but mostly as Primal Dialga. In the future, because of the collapse of the Temporal Tower, Dialga has lost control of itself and has entered a state of self-preservation, keeping time frozen and refusing to let it flow properly. When the player and partner return from the future and arrive at the collapsing Tower, they must beat almost-Primal Dialga in battle and restore the Tower. After putting some sense into it, Dialga is so grateful that it revives the player (who was erased from existence). After going back to Dialga at the top of Temporal Tower, it decides that the player wants a rematch. Once defeated, Dialga joins the player's team. In the Sky-only Special Episode In the Future of Darkness, after the final battle between Primal Dialga and the trio of Grovyle, Dusknoir and Celebi, all of them start to disappear due to the past finally being changed by the player, but are saved by an implied higher being than Dialga, who also restores Dialga to its normal state.
Pokémon Ranger: Guardian Signs: Dialga appears in the optional Ranger Net extra mission Pledge to Arceus. It must be captured along with its counterparts Palkia and Giratina in the Sky Fortress to access Arceus.
The forms differ in their base stats: Dialga's Origin Forme has decreased Attack and increased Special Defense compared to its standard form, though its base stat total is the same. In Legends: Arceus, its signature move, Roar of Time, has modified base power and accuracy when used by its Origin Form, as well as a unique animation.
The gem on Dialga's chest resembles a Prism Sphere.
The spikes on Dialga's back, at a certain point of view, look similar to a Time Gear. In the anime, when Dialga uses Roar of Time, the spine extends and the five spikes become thinner and more pronounced.
Dialga is the only Legendary Pokémon to have a role in four different movies.
According to Junichi Masuda's blog, the Spanish translation team suggested changing the name Dialga because of its similarity to the Spanish word alga (algea).
Dialga, along with Palkia, may be based on the Shinto legend of Izanami and Izanagi, who are said to have created one island with a spear, erected a pillar on it, and from there created the islands of Japan. Appearance-wise, Dialga seems to be based on short-necked sauropod dinosaurs such as Camarasaurus or Brachytrachelopan. The turquoise pattern on its body is vaguely reminiscent of clock hands, where the ends of the "clock hands" are diamond-shaped.
Its Steel type is likely to come from the concept of adamant, which is an archaic word for diamond, meaning "unconquerable", where the qualities of hard metal (probably steel) were attributed to it. It is also possibly due to the hardness of diamonds, the fact that metal is known to last long periods of time, or the fact that most parts of a clock are made of metal, such as the gears. It may also be because diamonds are compressed carbon, and steel is an alloy from iron and carbon. Metaphorically, it could be a reference to the rigid and unaltering pattern of passing time, as metals are known for their resilience against physical forces. The Steel-type might also represent the solid state of matter, whereas Palkia's Water-type represents the liquid state and Giratina's Ghost-type represents the gaseous state.
Dialga's Origin Forme appears to be based on Arceus. Like with Arceus, it may be based on a qilin or Longma, as it possesses both equine and dragon-like qualities, the latter of which are more pronounced in Dialga's case due to its Dragon typing.
Dialga may be derived from diamond. It may also involve día (Spanish for day, referring to the unit of time) or dial of clock dial and sundial.