Answer:
I am free for the taking. Through all of your life, though given but once at birth. I am less than nothing in weight, but will fell the strongest of you if held.
I follow the orders of only two. I respect the work of only two. I am in constant battles with many, Though one surpassed them all. With forces joined, We created hell, Until our mutual enemy fell. Who am I?
What is that which, though black itself, enlightens the world without burning?
If you drop me I'm sure to crack. But give me a smile and I'll always smile back.
A man shot two arrows at its center and missed both times, but using a sword swung once at its center and hit it twice.
People take me on walks and I run and have fun. What am I?