NEW YORK -- It was a particularly emotional moment at this week's funeral Mass for Jacqueline Kennedy Onassis when Maurice Tempelsman rose to read the poem he had selected. Titled "Ithaka," it spoke of discovery and of life's journey, and Tempelsman added his own sorrowful coda about a journey that had been too short. "So farewell, farewell," he concluded.

"Everyone was deeply moved," one of the mourners in attendance said afterward. "He read as if he'd written the poem himself. It was so personal, so heartfelt."

For the co-workers, friends and family inside the limestone church, Tempelsman had become a familiar figure, someone they would expect to participate in the service, to stand at Onassis's grave site with her children. But to those who knew Tempelsman only from magazine photos of him and Onassis strolling through Central Park, the captions generally identifying him as her "companion" or "friend," he was more enigmatic. It took her death to fully reveal the central role that the very private Tempelsman -- a man who shared her home, though a man who remains married to another woman -- had come to play in her life.

They were the same age, 64, though her enduring loveliness and his stocky plainness made him appear older. They shared many things: summers on Martha's Vineyard, interests in art and antiquities (Tempelsman is a collector), fluency in French, an aversion to publicity. In the public mind, Tempelsman must possess special qualities to have attracted such a regal and celebrated woman. But his admirers, who are many, can see the relationship the other way around: Onassis must have been far more than a famous beauty to have intrigued such a cultured and scholarly man. "It shows her seriousness and the depth of her intellect," says Phil Baum, acting head of the American Jewish Congress, where Tempelsman has been an active trustee.

"For those of us who cared about Mrs. Onassis, it was comforting -- it was terrific -- to know she was with somebody who was a good, generous and gentle man," says Roger Wilkins, who was an Agency for International Development administrator during the Kennedy Administration and has known Tempelsman for years.

A Belgian-born Jew, Tempelsman and his family fled Europe in 1940 and came to New York, where his father established a diamond brokerage. The industry has always been dominated by families, and Maurice joined his father's firm as a teenager, just as two of his three children and a son-in-law have joined his.

He is chief executive officer of Lazare Kaplan Inc. (1993 gross sales: $166 million). Headquartered on Fifth Avenue, it is one of the largest U.S. companies specializing in the import, cutting and sale of diamonds; its customers include Tiffany and Cartier. Tempelsman is also the general partner of Leon Tempelsman & Son, which has investments, mining and mineral trading interests around the world, particularly in central and western Africa.

Africa has been an abiding interest; Tempelsman has friendships and business alliances of 30 years' duration there, glides easily through its political and economic circles, is a connoisseur of African art. "He's a player in that scene," says Chester Crocker, former assistant secretary of state for African affairs. Until Wilkins succeeded him several months ago, Tempelsman served as chairman of the board of the nonprofit African-American Institute, which fosters African development and cooperation between Africans and Americans.

In terms of wealth, Tempelsman is not in the Aristotle Onassis league: By Forbes magazine's calculations, his personal worth didn't reach the $300 million threshold needed to land on the Forbes 400 list of the richest Americans. He is a prosperous man nonetheless. That was his 70-foot yacht, the Relemar, berthed at the Vineyard, on which Jacqueline Onassis hosted the vacationing First Family last summer; Tempelsman was at the helm.

He met Jacqueline Kennedy when she was still a young senator's wife and he was supporting JFK's presidential aspirations. Tempelsman has long been generous to Democratic Party candidates, last year contributing more than $83,000 to the Democratic National Committee, the Democratic Senatorial and Congressional campaign committees, and individual campaigns.

But it was apparently not until after Aristotle Onassis's death in 1975, with the twice-widowed Jacqueline living in New York, that they began spending time together. Tempelsman was one of the financial advisers who helped her multiply the reported $26 million settlement she received after Aristotle Onassis's death. Published estimates of Jacqueline Onassis's wealth have varied wildly -- $100 million? $200 million? "His counsel resulted in increasing her assets substantially," was all a discreet Tempelsman spokesman would say.

By the early '80s, though Tempelsman described himself in a Fortune interview as a family friend, he and Onassis were quietly but unmistakably a couple, seen at small dinner parties and low-key cultural events. According to the spokesman, Tempelsman moved into Onassis's rambling Fifth Avenue apartment overlooking Central Park about 1988. His wife of more than 40 years, Lily, lives across the park on the Upper West Side.

Yet it was rare to hear or read a word of opprobrium about Tempelsman and Onassis's relationship, even from New York's cattier columnists and insatiable tabloids, which never tired of running her photograph. It was almost as though the press and public had decided she was entitled to grow old with someone. His acceptance by her family probably helped quiet criticism; "John and Caroline have come to feel quite close to him," his spokesman says.

"They were a well-matched and distinguished couple," says Vivian Lowery Derryck, president of the African-American Institute. Onassis occasionally accompanied Tempelsman to small institute dinners with African leaders. His demeanor toward her was unfailingly "comfortable, respectful and loving," Derryck says. "And she respected and admired him and held him in great affection."

As Onassis's illness progressed, Tempelsman was omnipresent, escorting her home from the hospital, supporting her on her last walks through the neighborhood, keeping vigil by her bedside with her children as she died. Friends say they have sent notes of condolence but have not wished to intrude on his evident grief.

Perhaps inevitably, Tempelsman's long immersion in African politics and the diamond trade, along with the occasional display of domestic political muscle, have lent him an air of intrigue. In 1990, for example, The Washington Post reported that former representative Mervyn Dymally (D-Calif.), a leader in seeking economic sanctions against South Africa, had changed his position on diamond imports after a 1988 meeting with Tempelsman -- and after Tempelsman's $34,200 contribution to a Dymally-supported scholarship fund for minority students. Dymally denied soliciting the contribution or being influenced by it; Tempelsman also said that the contribution and Dymally's shift were unrelated.

"There are people who think, and have alleged, that because Maurice has been involved in that business in Africa for years, he's a bad fellow ... {that} he can't be in that business and be a person who is always honorable," Wilkins says. But Wilkins and Derryck describe Tempelsman as a strong supporter of African liberation and democratization, who helped underwrite Nelson Mandela's first visit to the United States.

More personally, they and other friends and associates portray a man of Old World courtliness, courtesy and erudition. "You know from what he says, as well as what he doesn't say, that there's a lively and fertile mind operating there," Crocker says. "This is a world citizen we're talking about, at home in almost any culture he finds himself in."

What did Jacqueline Onassis see in him? "I was a receptionist, and he had every right to ignore me," says a young woman who worked at one of Tempelsman's companies several years ago. "But he was so warm, so friendly. ... He's the kind of person whose eyes twinkle when he speaks to you." She never wondered why they were together.