Final answer:
Marcus Garvey was the leader who promoted the 'Back to Africa' movement and founded the Black Star Steamship Line to transport African Americans back to Africa.
Step-by-step explanation:
The individual known for his slogan 'Back to Africa' and who bought a fleet of ships to transport those willing to go back to Africa was Marcus Garvey. Garvey, a Jamaican immigrant and leading figure in the early 20th century, founded the Black Star Steamship Line and the Universal Negro Improvement Association (UNIA) to empower African Americans and promote the idea of returning to their ancestral lands. Although his plans were visionary, they were marred by financial mismanagement and legal troubles, leading to imprisonment for mail fraud and later deportation. His efforts, despite their flaws, laid the groundwork for future civil rights movements.