Which president in the 20th century did not appoint a justice to U.S. Supreme Court?

The only president serving in the 20th century not to appoint a justice to U.S. Supreme Court was Jimmy Carter. All the other presidents serving in the 20th century appointed at least one Supreme Court Justice. President Carter was the only full term president not to have the opportunity to select a justice. Just a few months after Carter left office, Potter Stewart resigned, opening up the seat taken by O'Connor. Stewart had been appointed by President Eisenhower. Like many other justices, Stewart apparently timed his resignation so that a president of his own party could select a replacement.

Supreme Court justices, court of appeals judges, and district court judges are all nominated by the President and confirmed by the United States Senate, as stated in the Constitution. Accordingly, concerning federal judges appointments, President Carter in total appointed 259 federal judges, including 56 judges to the courts of appeals and 203 judges to the United States district courts.

So, although Carter made no appointments to the U.S. Supreme Court, two of his court of appeals appointees - Stephen Breyer and Ruth Bader Ginsburg - were later appointed to the Supreme Court by President Bill Clinton.