“Whose woods these are I think I know...” begins a poem by which American author?

My f-I-l used this phrase for his password, using the 1st letter of each word. I did not know it was from a poem.

It's a very lovely poem indeed. I have read it many times. I feel pleasure by reading it. Robert sir is a great poet really. He will be immortal in the field of literature.

He wrote this poem at a time in his life when he was dealing with depression to the point of suicidal thoughts, “the darkest evening of the year.” That’s what it’s about.