Answer:
Walt Whitman, ‘Song of Myself’.
Explanation:
I celebrate myself, and sing myself,
And what I assume you shall assume,
For every atom belonging to me as good belongs to you.
I loafe and invite my soul,
I lean and loafe at my ease observing a spear of summer grass …
So begins this gloriously expansive nineteenth-century poem. When Whitman’s 1855 volume Leaves of Grass was published at Whitman’s own expense – the first edition containing just a dozen untitled poems – ‘Song of Myself’ headed the collection. This statement of selfhood contains the famous line ‘I am large, I contain multitudes. The link above takes you to several choice excerpts from the longer poem.