|Base item||war hammer|
|Damage vs. small||1d4+1 x2|
|Damage vs. large||1d4 x2|
|Base price||200 zm|
Ogresmasher is an unaligned war hammer that does +1d5 to hit and double damage against ogres. Since it's based on a weak base item, and does its extra damage to a class of monster that's neither particularly common, nor especially dangerous, Ogresmasher is often considered the most worthless artifact weapon. (A regular +0 long sword does more damage to ogres than +0 Ogresmasher, and given its extremely limited use, enchanting it would be foolish.)
In 3.6.1, Ogresmasher will also set the wielder's CON to 25, making it only very slightly less pointless - a character with 25 CON will gain 1 more HP per level over a character with 18 CON, and at level 11 or above, regenerate slightly more HP depending on the character's experience level (up to 3.1 HP per three turns at level 30).
In dNetHack, it can be two-weaponed with and also grants warning versus ogres, in addition to instakilling ogres. Characters in dNetHack who aren't capable of two-weaponing and have no need of the second weapon slot can get increased max HP by keeping Ogresmasher in the off-hand. The 25 CON will grant a 14 CON character around 5/3 as much health, since it applies retroactively to all health gained from leveling up.