The Hobbit when all hope seemed lost in chapter 17 who appeared on the scene to help?

In Chapter 17 of The Hobbit, "The Clouds Burst," when all hope seemed lost and the dwarves were trapped by the giant spiders in Mirkwood, Beorn appeared on the scene to help.

He is a powerful shapeshifter who could turn into a bear, and his arrival was a turning point in the story, as he single-handedly drove back the spiders and saved the dwarves.