Reshiram is a large white, draconian Pokémon that represents truth (while its counterpart, Zekrom, represents ideals). Reshiram has a slightly mammalian-looking face that resembles that of a white lion. It has a great wispy flowing mane of white feathery fur surrounding its head, striking blue eyes, and several silvery-white rings around its thin, swan-like neck. It has a large cylindrical torch-like tail which functions as a powerful fiery engine. It has with a single silvery band around each of its hands, which are attached to its wings. Its arms are attached to its wings, which are vast and feathery. Its chest feathers resemble the design of the Silver Wing. The lower portion of its body protrudes outward to a point. It has a round belly and thick, powerfully-built legs with three claws on each foot, and a single claw on the back of each foot.
It's revealed in Black and White 2 that Kyurem, along with Zekrom and Reshiram were all part of a single Pokémon.
Reshiram is the only known Pokémon with a permanent Fire and Dragon typing. The only other Pokémon with this typing is Mega Charizard X.
Reshiram's name appears to have originated from the Japanese word "shiro" which means "white", referencing its color.
Reshiram, along with Zekrom and Kyurem is part of the Tao Trio. Reshiram embodies dynamism.
Reshiram is the first Fire-type Pokémon that is not weak to Water, and arguably the only one for now.
As stated above, Mega Charizard X has the same Fire/Dragon typing as Reshiram and is therefore neither weak nor resistant to Water, but opinions vary over whether or not it counts as a separate Pokémon, being a Mega Evolution.
Volcanion not only has a unique Fire/Water typing that is not weak to Water, but it is also the only Fire-type Pokémon with an ability granting it immunity to Water, in this case, Water Absorb. However, Volcanion is still considered by many to be technically unreleased.
In Movie 14, Reshiram has the same roar as the monster Megaguirus, from the Godzilla franchise. Originally, this roar was Zekrom's, but for Movie 14, Zekrom was given the roar of Baragon, also from the Godzilla franchise. Megaguirus' roar had previously been used in Movie 11 when Zero's fighter released an attack.
Reshiram also appears in a Dream World minigame; if the WIFI Reshiram from the White version game is sent to the Dream World, in the special home Victini appears to the player, and in the minigame's intro, Victini fails to destroy the barrier alone, so the player must ask his/her WIFI Reshiram to help destroy the barrier by collecting power ups, and at the end, Reshiram destroys the barrier by using a flame attack.
It protects the PokéPark in PokéPark 2 while Zekrom protects Wish Park.
In Hyperdimension Neptunia, a DLC weapon for Ram, the Staff of Ideals, is based on Reshiram when fused with Kyurem.
Reshiram's Dream World Art
Reshiram's 3D Model seen in PokéPark 2: Wonder's Beyond
Reshiram's TCG Art
Reshiram and Zekrom representing the concept of Yin and Yang