The great-grandson of a slave, i argued the case against "separate but equal" and against brown v. board of education before the supreme court. i won. this was the beginning of a tremendous change in the united states. who am i?

The answer is Thurgood Marshall.

Thurgood Marshall was an Associate Justice of the Supreme Court of the United States from October 1967 to October 1991, being the first African-American elected to the post.

Before becoming a judge he had a successful career as lawyer, with a high success rate before the Supreme Court, and known for his victory in the case Brown v. Board of Education. In 1967, he was appointed by President Lyndon Johnson to the Supreme Court of the United States.