Final answer:
Frederick Douglass was the former slave who wrote an autobiography and became a leading abolitionist orator.
Step-by-step explanation:
The former slave who wrote an autobiography and became a leading abolitionist orator was Frederick Douglass. Douglass was born into slavery in Maryland and later escaped to the North. He published his autobiography, 'Narrative of the Life of Frederick Douglass, an American Slave,' which detailed the harsh realities of slavery and became a bestseller. Douglass also traveled extensively, delivering powerful speeches on the abolition of slavery and advocating for equal rights for African Americans.
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