After defeating Al Gore, this quest will automatically appear in your list. Head to the church and find it hiding in the church yard. Engage it in battle.
It has considerable HP and exceptional defense as well. The only way you surely win is by exploiting it with multiple status ailments. Block his powerful attacks. Later it he will use Cry of the ManBearPig which will allow him to regenerate much more HP than your status ailments can deal.
You can't deal that much damage to him because of his insane armor rating. Bleeding works exceptionally well along with Burning and Grossed Out so make sure you have melee and ranged weapons that can accommodate the necessary weapon strap-ons to inflict these effects.