In chapter 7, what do we learn about Beorn?

In Chapter Seven, we learn that Beorn is a skin-changer.

"Yes it certainly is! No I could not! And I was explaining very carefully," answered the wizard crossly. "If you must know more, his name is Beorn. He is very strong, and he is a skin-changer."

"What! a furrier, a man that calls rabbits conies, when he doesn't turn their skins into squirrels?" asked Bilbo.

"Good gracious heavens, no, no, NO, NO!" said Gandalf. "Don't be a fool Mr. Baggins if you can help it; and in the name of all wonder don't mention the word furrier again as long as you are within a hundred miles of his house, nor, rug, cape, tippet, muff, nor any other such unfortunate word! He is a skin-changer. He changes his skin; sometimes he is a huge black bear, sometimes he is a great strong black-haired man with huge arms and a great beard. I cannot tell you much more, though that ought to be enough. Some say that he is a bear descended from the great and ancient bears of the mountains that lived there before the giants came. Others say that he is a man descended from the first men who lived before Smaug or the other dragons came into this part of the world, and before the goblins came into the hills out of the North. I cannot say, though I fancy the last is the true tale. He is not the sort of person to ask questions of.