Final answer:
William Lloyd Garrison was a radical abolitionist who believed that slavery contradicted the core principles of the Declaration of Independence and advocated for immediate emancipation through his publication, The Liberator, and the establishment of the American Anti-Slavery Society.
Step-by-step explanation:
William Lloyd Garrison viewed the issue of slavery as fundamentally opposing the ideals of the Declaration of Independence, which declared that "all men are created equal" with certain unalienable rights. He believed that African Americans had a natural right to liberty and the pursuit of happiness, and thus, slavery was a moral abomination that needed to be abolished immediately.
Garrison's advocacy was channeled through his newspaper, The Liberator, and he was instrumental in the establishment of the American Anti-Slavery Society, which based their mission for immediate emancipation upon the Declaration of Independence and divine revelation, strongly criticizing the U.S. Constitution for perpetuating slavery.