A.He was a slave who argued he was free.
Dred Scott was a slave, who is very well known for the Dred Scott v. Sandford Case, in which he filed suit in the court for his freedom in 1847, alleging that his residence in Illinois (a free state) and the Louisiana Territory (where slavery was prohibited) from 1830 to 1840 approximately should make him a free man.
Despite his efforts and bravery, the Supreme Court on March 6, 1857, denied his freedom alleging that black people didn't have the right to sue in federal court because they weren't American citizens. And, unfortunately, Dred Scott remained a slave.