Dialga did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Dialga (Japanese: ディアルガ Dialga) is a dual-type Steel/Dragon Legendary Pokémon.
It is not known to evolve into or from any other Pokémon.
Dialga is the version mascot of Pokémon Diamond, appearing on the boxart.
Along with Palkia and Giratina, it is a member of the creation trio of Sinnoh, representing time.
Dialga is a dark blue sauropod-like Pokémon with some gray metallic portions, such as its chestplate, which has a diamond in the center. It also has various light blue stripes. It has a fin-like structure on its back and a crest on its head, resembling a dinosaur. Dialga also has two horns on top of its head, two fang-like horns around its mouth, three spines on the back of its neck, long claws, and a short tail. The wing-like structure on its back can be used to focus the flow of time, as seen in Explorers of Time, Darkness, and Sky.
Dialga can warp time by either speeding it up, slowing it down, or stopping it altogether. As Dialga primarily resides in a different dimension, its behavior is nearly impossible to study. 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 that can learn Roar of Time.
In games prior to Pokémon Omega Ruby and Alpha Sapphire, Dialga has a catch rate of 30.
No other Pokémon shares the same type combination as Dialga.
Dialga is the tallest Generation IV Pokémon.
Dialga is tied with Blade Forme Aegislash for the highest Special Attack base stat of all Steel-type Pokémon.
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 second Pokémon in the Pokémon Mystery Dungeon series to feature an alternate coloration that is not its Shiny coloration, the first being Kecleon.
Although Dialga is genderless in the main games, it is referred to as a male in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness.
Dialga is the first Legendary Pokémon to have a role in three different movies.
According to Junichi Masuda's blog, the Spanish translation team suggested changing the name Dialga because of its similarity to the word alga, seaweed.
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. Its type is Steel possibly due to the hardness of diamonds, 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 a alloy from iron and carbon. Its turquoise pattern on its body is vaguely reminiscent to clock hands, where the ends of the "clock hands" are diamond-shaped.
Dialga is derived from diamond. Ga may be a corruption of gon from dragon. It may also involve dia (Spanish for day, referring to a unit of time) or dial (as in sundial, an instrument used to tell time using shadows on a clock face).