The answer to the crossword puzzle for the term 'Humphrey's Successor' is AGNEW, a 5-letter word. Spiro AGNEW was the Vice President of the United States under President Richard Nixon from 1969 to 1973. He was the first Greek American to hold the office and the second Vice President to resign from office. AGNEW succeeded Hubert Humphrey, who had been Vice President under President Lyndon Johnson from 1965 to 1969.