Is nature the most important dramatis personae in "King Lear"?
In her essay "Representations of Nature in Shakespeare's King Lear," Sarah Doncaster states that the concept of nature is the foundation of the play:
From Kingship through to personal human relations, from representations of the physical world to notions of the heavenly realm, from the portrayal of human nature to the use of animal imagery; Nature permeates every line of King Lear.
I'm not sure I would call nature a character. It does not act by itself; that is, nature is manipulated by Lear and mirrors his mental state. The more mad, or "unnatural," Lear seems to be, the more harmful are the forces of nature. I would say Lear himself is the most important character.