Paul B. Fay Jr., confidant of President Kennedy; at 91

The cause was complications of Alzheimer’s disease, said his daughter Katherine.

Mr. Fay, known as Red for his striking mane, recuperated with Kennedy after both their PT boats were hit by the Japanese. He repeatedly campaigned for Kennedy, beginning with his first run for Congress in 1946. He was an usher at Kennedy’s wedding.

After Kennedy became president, it was with Mr. Fay that he sneaked out to see “Spartacus’’ at a Washington movie theater. The men and their wives vacationed together. Attending Mass after being inaugurated, Kennedy asked Mr. Fay to pass him $10, saying he wanted Americans to know they had “a generous president.’’

In an interview on Monday, Theodore C. Sorensen, President Kennedy’s special counsel and biographer, called Mr. Fay one of the president’s two or three best friends.

“He made JFK laugh,’’ Sorensen said. “He was absolutely loyal and devoted to JFK.’’

Mr. Fay, a Republican who had supervised at most 100 workers at his father’s construction company, was rewarded with the number two job in the Department of the Navy, helping oversee 1 million military and civilian employees. Defense Secretary Robert S. McNamara had initially opposed the appointment.

But Kennedy treasured old friendships.

In their book “Johnny, We Hardly Knew Ye’’ (1972), the Kennedy confidants Kenneth P. O’Donnell and David F. Powers, writing with Joe McCarthy, said Kennedy’s personal friends during his last 10 years had all been longtime friends from the 1930s and 1940s.

Kennedy said at a news conference in 1962: “The presidency is not a very good place to make new friends. I am going to keep my old friends.’’

Part of the basis for the friendship was Mr. Fay’s role as a kind of court jester. In an interview with Sally Bedell Smith in her book “Grace and Power: The Private World of the Kennedy White House’’ (2004), Rowland Evans, the columnist, said, “He loved the banter, and Red Fay had that.’’

The president also knew he could speak to Mr. Fay in complete confidence. After the failed invasion of Cuba by Cuban exiles at the Bay of Pigs, Mr. Fay recounted later, Kennedy told him that the ill-planned, US-supported operation showed that he could not depend on the top military brass.

Nor, Kennedy said, would he yield to the “fanatical fringe’’ who admonished him for not using more force. He even said he was so discouraged that he might not run for a second term.

That and other revelations came in Mr. Fay’s 1966 book “The Pleasure of His Company.’’ It was one of the first biographies published after Kennedy was assassinated in 1963, and Mr. Fay had agreed to let Robert F. Kennedy, the president’s brother, and his widow, Jacqueline, read it before publication. They objected to its candor, as well as to what Jacqueline Kennedy deemed vulgarities.

Mr. Fay rejected most of the proposed changes.

In an interview on CNN in 2003, Hugh Auchincloss, Jacqueline Kennedy’s stepbrother, praised the book, saying it was the best one written about President Kennedy.

Paul Burgess Fay Jr. was born in San Francisco, into a large, wealthy Irish Catholic family, not unlike the Kennedys. He graduated from Stanford in 1941 and joined the Navy soon after the Japanese attack on Pearl Harbor.

He met Kennedy at PT Boat School in Rhode Island. In the South Pacific, each skippered a boat.

Mr. Fay was awarded the Bronze Star after his was run down by a Japanese destroyer.

After the war, Mr. Fay visited Kennedy and his family in Palm Beach, Newport, and other places. Kennedy even hoped that Mr. Fay would marry one of his sisters.

“He was kind of lining me up with Eunice,’’ Mr. Fay said in an interview for “The Kennedy Women: The Saga of an American Family’’ (1994) by Laurence Leamer.

Mr. Fay married Anita Marques, whom Kennedy and other PT boat veterans always called “the bride’’ even before they were wed. He leaves her, along with his daughter Katherine and another daughter, Sally Fay Cottingham; his son, Paul III; seven grandchildren; and a great grandson.

After his Washington years, Mr. Fay was an investment banker in San Francisco, a supporter of charities, and a sought-after public speaker.

A favorite story involved the time in July 1960 when he was golfing with Kennedy, whose tee shot was rolling straight for the hole. “Go in!’’ Mr. Fay yelled.

But Kennedy was overjoyed when the ball hit the pin and caromed away. He firmly informed Mr. Fay that his political career might have ended if word had spread that another golfer wanted to be president. Political cartoonists had lampooned the strong interest that his predecessor, Dwight D. Eisenhower, had with the game.

In his book, Mr. Fay remembered a sunny Friday afternoon when he was sitting next to Kennedy on Air Force One. The president gazed at the clouds and said, “Redhead, we travel pretty well.’’

Then he added: “But let’s enjoy it. It’s not going to last forever.’’