Final answer:
Walt Whitman, who was prolific in the 1800s, is considered the most popular American poet of that century. His works, including 'Leaves of Grass' and 'Song of Myself', celebrated the common man and introduced free verse into American literature, establishing new ways of poetic expression.
Step-by-step explanation:
The most popular American poet of the 1800s was Walt Whitman, a man who built a reputation through his dynamic and innovative works. As a poet, Whitman held various jobs such as a journalist, newspaper editor, and civil servant, but literature was his true calling. His poetry, especially Leaves of Grass, which was first published in 1855, and the well-known Song of Myself, celebrated the common man and utilized a common language that was accessible to all. Whitman's writing did not conform to traditional rhyme and meter; instead, he introduced free verse into American poetry, and his focus on the ordinary and the universal human experience made him the journeyman poet of Americanness.
Whitman's love for the 'common people' shone through his writings, and he firmly believed that the true 'genius of the United States' was not found in its executives or legislators, but 'always most in the common people'. His works helped marry embedded cultural forms to the needs of a rapidly modernizing nation, and through this, he achieved great success and remained influential beyond his time. Whitman also established free verse's potential in English-language poetry, employing it to explore a broad range of topics while offering a more flexible form that could adapt to the diverse experiences encapsulated in his verse.