A Dragon/Electric Legendary Type Pokemon of the Unova Region. Zekrom is known as the Deep Black Pokemon.
In one of the legends of the Unova Region it is said that Zekrom and Reshiram were once a single powerful Dragon Pokémon used by two brothers who ruled the region. However, the brothers' rule caused great conflicts as they fought over how best to rule the nation and, due to the fighting, the dragon was split into two separate Pokémon. Each dragon resided with its respective master, Reshiram with the older brother and Zekrom with the younger brother. It was then foretold The brothers then fought in a endless battle that would have destroyed the region of Unova. To end the fighting the People of Unova decided to put both dragons into a deep sleep causing them to turn into a Stone matching their color. They were then placed inside the Dragon Spiral were they slept until awakened.
Zekrom is able to be caught in Pokemon White when the player is about to confront N and Reshiram. In Pokemon Black, Zekrom is awakened by N and is under his control. Zekrom is able to use two signature moves known as Fusion Bolt and Bolt Strike.
Zekrom made its first appearance in the first episode of Pokemon: Best Wishes. After Ash and Pikachu arrived in the Unova (Isshu) Region and are attacked by Team Rocket, Zekrom appears hidden in a lightning cloud where it hits Pikachu with one of it's Lightning Bolts causing it to lose it's electrical powers. Towards the end of the episode, Zekrom appears again over Professor Juniper's Lab and gives back Pikachu's powers. With it appearing in the anime it is speculated that Zekrom and Reshiram were awakened from their sleep by somebody.