Zekrom

Zekrom is a dual-type Dragon/Electric legendary Pokémon and serves as an antagonist in some of its appearances.

Pokemon Conquest
In Pokemon Conquest Zekrom is Nobunaga's Pokemon.

Pokemon Black
Zekrom serves as N's Legendary Pokemon.

Pokemon Black: The Movie
Sometime during the three years he spent traveling the world prior to the events of the film, Damon happened to overhear Zekrom calling to him while he observed the ruined Kingdom of the Vale alongside Mannes. Together, the two of them went down into the caves inside the Sword of the Vale, where they became separated. At the bottom of the cave Damon discovered the Dragon Stone containing Zekrom and reawakened it.

With Zekrom's help, Damon traveled to the villages of the People of the Vale and managed to convince them to support him. Its first appearance in the film comes when it helps Damon destroy a giant iceberg that threatens to destroy Glacine's village in a polar region. It later appears in a flashback as Damon tells the story of his travels. When he raises the Sword of the Vale and comes to be opposed by Ash, Cilan, Iris, Carlita and Juanita, Damon summons Zekrom to aid him. It battles Juanita's Golurk, which Zekrom easily defeats. The second time it fights Golurk, it is interrupted by Reshiram, which Ash has discovered and allied with. The two dragons battle after Reshiram drops Ash at the castle, ending in Zekrom's defeat. Zekrom and Reshiram then realize that Damon's actions have unleashed a corrupted Dragon Force that threatens to destroy the world, and both dragons blow away the clouds to reveal this fact to Damon.

Pokemon Adventures
In the manga Pokemon Adventures, N used Zekrom to defeat the Elite Four and Champion, Alder, and tried battling Black and Reshiram. However, N and Zekrom were defeated.