The Kneecapper

The Capper, also known by the name of Knee-Capper and officially known by the name of War Hammer +1, +4 vs. giant humanoids, is a war hammer +1 with +4 bonus to thaco and damage when wielding this weapon against ogres and giants. It has a weight of 8 lbs and a speed factor of 2. Ashineeda and this weapon are the strongest war hammer available in the game of Baldur's Gate. They both have the same speed factor, but Ashineeda is against any monster more powerful, expect for giants and ogres.

In-game description
"War hammer +1, +4 vs. giant humanoids: The Knee-capper, or 'The Capper', as it is affectionally known in dwarven circles, is rumored to have been forged by Clangeddin himself. He gave to a small clan of homeless dwarves that they might carve a place for themselves amongst the giants and ogres in their area. The hammer has been passed from hero to hero, occasionally finding its way into non-dwarven hands."