Zekrom is a black, bipedal Pokémon resembling a saurian winged dragon, with a primarily charcoal-colored hide and pure black 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 extend 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. Its tail consists of a large, round, conical, and spiked formation, with a black inner portion and bands on the tip of the outside portion. When its emotions surge, Zekrom activates Overdrive mode, and its tail lights up with a blue light.

In Unovan legends, Zekrom and were created from a single dragon Pokémon commanded by the twin heroes of Truth and Ideals when it split into two. Zekrom assists anyone who wants to create an ideal world, so it allied itself with the younger brother, whereas Reshiram sided with the older brother, who sought the truth. The two dragon Pokémon battled each other, but were equally matched and unable to achieve victory, so the brothers ceased their conflict agreed that neither of them were right. However, their sons inherited their ideologies and resumed their clash; the Unova region was subsequently devastated by the combined might of the lightning and fire powers of Zekrom and Reshiram before the two Pokémon disappeared. Zekrom will transform into the Dark Stone should its body get destroyed or when attacked by 's tendril-like appendages. It can willingly revert back to normal when awakened by a hero who believes in ideals.

Zekrom flies throughout Unova while concealing itself in thunderclouds. It has a large generator in its tail that it uses to create electricity, which is powerful enough to scorch the world. Zekrom and Reshiram activate each others' tail generators when they use an enormous thunderbolt and an enormous flame, respectively, at the same time, powering up both attacks. When the inside of its tail spins in a motor-like fashion, it blasts its surroundings with several lightning blasts. It is said in mythology that Zekrom annihilates the kingdoms of people who have lost the righteousness in their hearts with its lightning. In Pokémon the Movie: Black - Victini and Reshiram and White - Victini and Zekrom (M14), Zekrom is shown to be able to speak through telepathy. It loves Zekrom Treats made by Snacksworth, who once encountered it in the past.

(Source: Bulbapedia)