Haxorus is a new dragon type pokemon in Pokemon Black and White. Haxorus evolves from a Fraxure at level 48, which evolves from an Axew at level 38.
Haxorus can not be caught in the wild, so you’ll have to either catch an Axew in Mistralton Cave and evolve it into Fraxure at level 38, and then into Haxorus at level 48, or catch a Fraxure on the outer region of Victory Road and evolve it into Haxorus at level 48.