Zekrom is a black, bipedal Pokémon resembling a dragon or dinosaur, with dark patches on various portions of its body. It has red sclerae, white irises, and black pupils, as well as a small horn-like protrusion on the tip of its snout. Its head sports a thundercloud-like crest tipped with light-blue coloration. There are six pairs of pointed teeth visible when its mouth is open, two in the upper jaw and four in the lower. At the base of its neck is a black, stud-like feature, and atop its shoulders are similar, larger features resembling armor padding. The bases of its wings also have such padding, and a fanned, splayed, seemingly webbed shape with a small "wing-spike" on one edge. The lower lengths of Zekrom's arms extenuate into splayed, seemingly webbed, somewhat baseball-mitt-like formations, with three-clawed, dark-colored hands on the undersides. The front portion of Zekrom's waist is black-colored, with its belly and thighs having thin striations down their length. Its knees are black, as are the foremost parts of its three-clawed feet and spiked heels. When its emotions surge, it enters Overdrive mode, and its tail lights up with a blue light.
Zekrom's tail consists of a large, round, conical, and spiked formation, likened to an electricity generator, with a black inner portion and bands on the tip of the outside portion. This tail produces energy for its attacks and emits an anti-gravity field, allowing Zekrom to fly through the air with minimal effects from aerodynamic resistance and gravity. This tail generator is also activated when influenced by either Fusion Flare or Blue Flare, which in turn powers up Zekrom's own Fusion Bolt or Bolt Strike, its signature moves. It can cause several thunderstorms in one area, and it normally hides in thunderclouds. It is said that Zekrom holds the power to destroy the world.
In a Unovan myth about the twin heroes, Zekrom sided with the younger brother who sought ideals. Zekrom is said to be Reshiram's equal in battle, meaning neither of the two dragons can truly defeat the other. Zekrom and Rehsiram are powerful enough to destroy the region they reside in. Zekrom can transform into the Dark Stone should its body get destroyed or by Kyurem's tendril-like appendages. Zekorm can willingly transform itself back from said stone when awakened by a hero who believes in ideals. According to one myth, Zekrom uses its lightning to annihilate kingdoms of people who have lost the righteousness in their hearts. It is a gender-unknown species.
Zekrom is the only known Pokémon capable of learning the move Bolt Strike by leveling up.
Zekrom debuted in the opening sequence of In The Shadow of Zekrom!. It made its full appearance later on, where it appeared above the skies of Nuvema Town. Its huge lightning bolt zapped Pikachu, making him unable to use his electricity. It reappeared in Enter Iris and Axew!, where Pikachu recovered his Electric powers after being zapped again by another of Zekrom's lightning bolts.
Zekrom appears on the Unova Pokémon League stage, where it will cover itself in a ball of lightning and hit the stage. Any fighters it touches will be damaged and if it hits the side of the stage, the stage will be tipped. It will also destroy the steps attached to the stage if there are any.
Zekrom trophy in Super Smash Bros. for 3DS
Zekrom also appears as a trophy in the 3DS game.
Zekrom's jet-black body contrasts sharply with the pure white of Reshiram, but the two do have some similarities: both are Legendary Pokémon said to have world-destroying powers. Zekrom's tail acts as a generator that can scorch the world with lightning, but it is said to assist those who wish to build an ideal world.
Zekrom was first revealed simultaneously alongside Reshiram on both the official English and Japanese Pokémon websites on May 28, 2010. This makes them the first two Pokémon simultaneously revealed worldwide.
On May 31, 2010, two weeks prior to the official revelation of Zekrom's type, Shōko Nakagawa spoke about her love of Electric-type Pokémon on her blog and mentioned that because of that, she wanted to get a Zekrom. This statement was then quickly removed.
In the Generation V games, Zekrom, Reshiram, and Kyurem use different variations of the same battle theme. In Pokémon Omega Ruby and Alpha Sapphire, and Pokémon Ultra Sun and Ultra Moon, however, Zekrom's version (featuring electric sound effects) is used for all three Pokémon.
Zekrom appears in Pokémon Battle Chess BW Version. Alongside Reshiram, the player must lose a specific number of pieces (three in Zekrom's case) to use it, and it takes four spaces on the board.
The initial design drafts for what would become Zekrom and its counterpart Reshiram were done by Keiko Moritsugu, while their final designs were created by Ken Sugimori.
According to Moritsugu, Zekrom's final design is mostly similar to her draft, while Reshiram's final design ended up being significantly different from her draft.
According to Junichi Masuda, Zekrom's design was originally supposed to have four hands.
Zekrom is Ken Sugimori's favorite Pokémon from Pokémon Black and White.
Zekrom and its counterpart Reshiram are based on the concept of yin and yang in Taoism, directly referenced by Zekrom's Japanese category name: こくいんポケモン Black Yin Pokémon. Zekrom's design was made to be tough and masculine, to contrast Reshiram's light, airy, graceful, and feminine design. Its masculine design, however, contrasts the traditionally feminine characterization of yin in Taoism. Its tail, the center point of its design, is based on an electric turbine.
Zekrom in its Dark Stone form may take inspiration from the Jewish concepts of Urim and Thummim (possibly translated as “light and perfection”). In pop culture, they are commonly depicted as a white and black stone. Its association with ideals would align with the idea of perfection.
Appearance-wise, it somewhat resembles a mid-sized to large theropod dinosaur, such as Allosaurus or Tyrannosaurus, and a European dragon. The crest on its head seems to be based on a thundercloud. The mythology about how Zekrom and Reshiram came about, regarding two brothers infighting, also bears some similarities to Romulus and Remus or Cain and Abel. There is also some resemblance to the Zoroastrian belief of two equally powerful deities, one representing light and truth, and the other representing lies and darkness. In this case, Zekrom can be taken to resemble Angra Mainyu, as opposed to Reshiram resembling Ahura Mazda, although Zekrom is not evil; rather it is an equally powerful opposing Legendary Pokémon.
Zekrom is derived from 黒 kuro (black). Ken Sugimori has also stated that Ze was used because it was a harder, stronger sound than Reshiram's Re, and Zekrom is a "powerful, strong character."