A wonderful warrior exists on earth.
Two dumb creatures make him grow bright between them.
Enemies use him against one another.
His strength is fierce but a woman can tame him.
He will meekly serve both men and women
If they know the trick of looking after him
And feeding him properly.
He makes people happy.
He makes their lives better.
But if they let him grow proud
This ungrateful friend soon turns against them.

A simple Google search returned your answer in less than 10 seconds.

Anglo Saxon Riddles (http://www.abdn.ac.uk/english/beowulf/riddle.htm)