In other words, there should be three independent resources confirming each pieces of questionable data. This cross-checking can be done different ways.
Answer:
The answer is Frederick Douglass. He wrote an autobiography entitled "Narrative of the Life of Frederick Douglass: An American Slave, Written by Himself." The book was written in 1845 and became a best seller. Consequently, it helped further the cause of abolitionism in the United States.
