Final answer:
The poem "O Captain! My Captain!" is an elegy that mourns the death of President Abraham Lincoln.
Step-by-step explanation:
The poem "O Captain! My Captain!" is an elegy, which is a poetic form that expresses grief and sorrow over the death of a person. These types of poems often commemorate the life and virtues of the deceased and seek consolation beyond the event. In this case, the poem mourns the death of President Abraham Lincoln and reflects on the impact of his loss. The use of repetitive phrases like "O Captain! My Captain!" and the tone of sadness throughout the poem are characteristic of elegies.