American financier. He was chairman of the board of the Postal Telegraph and Cable Corporation and president of the Mackay Radio and Telegraph Company. He was born on April 17, 1874 in San Francisco, California to Louise Antoinette (née Hungerford) Bryant Mackay (1843–1928) and John William Mackay (pronounced MACK-ee). His father was a silver miner and telegraph mogul who had been born in Dublin and emigrated to America with his parents. After arriving in America, his father died soon after, and John sold newspapers and got a shipyard job to support his mother and sister. Eventually, he went west, and with three partners, formed a mining corporation and discovered the "Big Bonanza" in Virginia City, Nevada, which became the largest single deposit of gold and silver ever found. More than $100 million dollars worth of gold (over $2.5 billion in today's currency) was extracted from that mine before it was exhausted in 1898, making all of them unimaginably wealthy. His father then married his mother and adopted her daughter by an earlier marriage. They lived between Paris and New York, where they brought up this daughter and their two sons, John and Clarence. Clarence sold his major source of income, the Postal Telegraph Company, to the new International Telephone and Telegraph Company (ITT) for an enormous amount of stock. The 1929 stock market crash wiped him out; he survived the Great Depression by selling his art and antiques. He was eventually reconciled with Ellin and her husband when he went to comfort her on the cot death of her baby; Irving Berlin always treated his father-in-law with respect and affection. Both Ellin Berlin and Clarence's granddaughter, Mary Ellin Barrett, were successful writers. Around 1897, Mackay met Katherine Alexander Duer (1880–1930), who was a beautiful debutante from an old, high society, New York family that he met on a steamship crossing between New York and England. She was a direct descendant of Lady Kitty Duer, daughter of Lord Stirling. They fell in love and were married on May 17, 1898. Harbor Hill in Roslyn, Long Island, the site of their future estate with the striking view of Hempstead Harbor, was Katherine's and Clarie's wedding present from the senior Mackays. Katherine oversaw much of the design and building of their mansion at Harbor Hill which was designed by Stanford White of McKim, Mead, and White and was the largest home White ever designed. Katherine was a suffragette and a champion of women's rights and became the first woman member of the Roslyn school board in 1905. Together, Clarence and Katherine were the parents of three children. In 1910, Katherine left Clarence and her three children to run away with Dr. Joseph Blake, the doctor who had cured Clarence's throat cancer. Blake then cured her eye cancer, and he in turn ran away with her nurse. The marriage officially ended in divorce in Paris in 1914. Katherine returned to New York in 1930, the same year she died from cancer. Because of religious convictions, he was a traditional Irish-American Catholic, Mackay would not remarry as long as his first wife, Katherine, lived. Therefore, Clarence and Anna Case (1888–1984) waited until after Katherine's death in 1930, and were subsequently married in 1931 at St. Mary's Roman Catholic Church in Roslyn, New York. His wedding gift to Anna was a platinum-set emerald and diamond necklace. The 167.97 carats (33.594 g) emerald was mined in Colombia and the necklace designed by Cartier. Anna was a lyric soprano who sang with the Metropolitan Opera and as a concert soloist. "Her life changed dramatically following an engagement to sing at a private musicale given in the home of Clarence H. Mackay (c. 1916). Taken with her beauty, he sent a carload of flowers to her at her next Carnegie Hall recital, enclosing a small diamond band with an enamel bluebird in the center." He died of cancer on November 12, 1938. His funeral was at St. Patrick's Cathedral where the New York Philharmonic played.

Bio by: Bobby Kelley