The Largest Giant
The Largest Giant is a unique monster in SLASH'EM that appears on his special level. He hits harder than other giants and has a ton of hit points. His corpse conveys fire resistance, oddly enough, and he resists stoning.
As a pet
The Largest Giant can be useful as a pet: he is very strong, hits quite hard, and more importantly, naturally hits monsters as a +3 weapon. This last property is necessary to harm many monsters in SLASH'EM, although it is not enough to hurt Vecna or the strongest A. He is quite easy to tame, given his low MR. Be sure to have a renewable source of taming (spell, harp) if you do though: he has a chance of spontaneously turning traitor.