Answer:
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.
Stealthy as a shadow in the dead of night, cunning but affectionate if given a bite. Never owned but often loved. At my sport considered cruel, but that's because you never know me at all.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.
My first master has four legs, my second master has two. My first I serve in life, my second I serve in death. Tough I am, yet soft beside. Against ladies cheeks I often reside.
Through its wounds, water does run. It once held many but now has none. What is it?
I am your mother's brother's only brother in law. Who am I?