Who was known as the two of greatest American poets?

There isn't a singular "two greatest" when it comes to American poets. It's a matter of personal taste and critical opinion, and many would argue for different figures.

However, some poets frequently cited as among the greatest American poets include:

* Walt Whitman: Known for his free verse and celebration of American democracy and the individual.

* Emily Dickinson: Known for her unconventional use of language and exploration of themes of death, love, and spirituality.

* Robert Frost: Known for his accessible and often poignant poems about rural life and nature.

* Langston Hughes: A central figure in the Harlem Renaissance, known for his powerful and often humorous poems about African American life.

* Sylvia Plath: Known for her confessional poetry and exploration of themes of madness, death, and the female experience.

* E.E. Cummings: Known for his experimental use of language and form.

Ultimately, the "greatest" American poets are a matter of subjective opinion. It's worth exploring the works of these and many other talented American poets to form your own conclusions.