In his office hangs a copy of the 13th Amendment, which abolished slavery in America. When his critics, and he has many, call him names, he likes to point to it and shout out, “I’m a free man!” This black history month is an opportunity to celebrate the most influential thinker on racial issues in America today—Supreme Court Justice Clarence Thomas.

Justice Thomas, who has been on the court nearly a quarter-century, remains a polarizing figure—loved by conservatives and loathed by liberals. But his “free”-thinking legal opinions...