Answer:
Dred Scott was born into slavery. He belonged to several landlords during his youth, including an army doctor, Dr. John Emerson. This one bought another slave named Harriet, that Dred Scott married with the agreement of Emerson.
At Emerson's death, the couple became the property of Emerson's widow, who denied them freedom despite the ban on slavery in Illinois where they lived at that time. Dredd then filed a lawsuit, aided by a local lawyer. In 1847 the St. Louis court ruled against Scott but was granted a second trial on the grounds that false evidence had been filed in the records. Three years later the jury decided that the Scott couple should be released because they lived in "free" territories. Widow Irene Emerson appealed, and the Missouri Supreme Court overturned the lower court ruling in 1852 on the grounds that "times have changed since the previous ruling." The couple was returned to their master's widow.
Irene Emerson married Dr. Calvin C. Caffee, an anti-slave member of Know Nothing. She transferred the slaves to her brother, John Sanford, who was a New York citizen. As the Missouri law at that time preached, the case should be brought to federal court because of the multiple naturalness.
With the help of new lawyers (including Montgomery Blair), Scott's lawsuit was filed in federal court. They lost, at first, and appealed to the Supreme Court, in the famous case that took its name. But, on the authority of Chief Justice Roger B. Taney, the Court ruled that the right to property prevailed and that blacks could not stand in trial as they were not citizens.
This judicial saga constituted a southern victory in their struggle for the maintenance of slavery. Without knowing it, Scott greatly contributed to divide the country, and was thus an important factor of the causes of the Civil War.