Answer:
Useful tool for who in darkness dwell. Within you, corrupting like a deadly spell.
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
What has one eye but cannot see?
Take off my skin, I won't cry, but you will.
It regulates our daily movements, but it feels no interest in our lives. It directs us when to come and go, but does not care if we pay attention. What is it?
People take me on walks and I run and have fun. What am I?