What is the dark Lugia Pokemon?

Dark Lugia the Pokemon that is on the cover of the Pokémon XD Gale of Darkness is known as Shadow Lugia in the American version of the game and in both versions it is referred to by its codename of XD001, the criminal organization of Team Cipher had corrupted a regular into the form of Shadow Lugia and Team Cipher had believed it to be the most perfect Shadow Pokémon that was completely healed from purification.