I simply cannot kill a dog. Also the axe is not a good reward compared to the helm

Why would you ask? Anyway, even if you kill his Tamriel incarnation (the dog) you won't kill the "real" one.

Yea I killed it before. The Axe was neat.

The axe has a fantastic design but nothing much else.

I've done it just to do both sides of the quest. Personally I don't usually do it.

i've killed him multiple times simply for bumping into me one too many times. stupid dog.

No I didn't choose to kill him, keeping him alive punished his owner way more then if I killed him haha, damn mutt drove me out of my mind.

I make a lot of characters. After about the 15th time I got that forced "talking dog" conversation, I wanted to kill that dog then and there.