From Anthony Summers’ biography of J. Edgar Hoover, Official and Confidential:
In September 1964, when King was due to visit the Vatican, Edgar’s friend Cardinal Spellman was asked by FBI not to grant King an audience. To Edgar’s astonishment, the Pope ignored the advice. Then came news that the civil rights leader was to receive the Nobel Peace Prize. King, in the hospital suffering from exhaustion, thought it “the foremost of earthly honors, not for himself but for the movement.” Edgar was beside himself with rage.
“The mores of this country has [sic] sunken to a new low,” he scribbled, overlooking the fact that the Nobel was awarded by foreigners. “He was the last one in the world who should ever have received it,” he said. “I held him in utter contempt…” King, Edgar thought, deserved only the “top alley cat” prize.
Bitterness was compounded by jealousy, for Edgar had long hankered after a Nobel himself. Herbert Jenkins, the longtime police chief of Atlanta, talked with him at this time. “For years and years,” Jenkins later revealed, “Hoover had tried unsuccessfully to win the prize. Many prominent Americans had been asked by Hoover to write the Nobel Committee … but every year Hoover was passed over … Then along comes a Negro southerner who is awarded the prize. It was more than Hoover could stand. It just ate away at him.”