I just noticed he isnt taking any damage when I backstab him. Has anyone seen him die?

Really, everyone else knew this??

hes invincible, and a Daedra

Do the Clavicus Vile quest and you can kill him

He seemed to be unkillable, but I had to get rid of him, as he was just too annoying. Always pushing me with his nose, making it impossible to search through shelves or line up a bow shot.

Shadowmere. Duh.

I did that quest a few days ago, he actually tanked a dragon for my mage, and he never got hurt. That dog is amazing.