The miniature is a War Priest from Avatars of War. I've 40K'd it up a bit, by adding a Plasma Gun, Combat Knife, ammo pack and purity seal, all taken from the Space Marine accessories sprue. The head is from a Space Wolf marine. A bit of etched brass on the shoulder and on the sides of the warhammer finishes him off (note that the base is temporary).
More pictures below.
