The poem “O Captain! My Captain!” is a tribute to:

The correct option is Abraham Lincoln.

“O Captain! My Captain!” is a famous metaphoric poem written by Walt Whitman in 1865. The poem was written as a tribute to the 16th President of the United States, Abraham Lincoln, following his assassination.
In the poem, Whitman uses the metaphor of a ship's captain who has successfully guided his vessel through a stormy voyage (representing the American Civil War) but falls dead on the deck just as the ship reaches the harbor safely. The "Captain" represents Abraham Lincoln, and the "ship" symbolizes the United States, which survived the Civil War under his leadership.