Wesley Williams keeps two unusual files in his office. Williams, the first African-American to make partner at D.C.’s Covington & Burling, has dubbed one file his “Vanitas Vanitatis” volume. It contains offers he’s received for leadership roles at corporations or in the government.

The other file contains a number of less-gracious notes, such as this one delivered last year: “What are you doing here? You should be back with your own kind.” Williams, who became a partner in 1975, says he has received, on average, one letter of that kind every year, for the past 30 years. He says he has found them slipped under his door at the office; on one occasion he received the communique through the U.S. mail. Williams, who believes the letters were probably sent by nonlawyers at the firm, is unfazed.