Wilson died early Saturday in Carmel Valley, Calif., where he had a home, his daughter Marcia Wilson Hobbs said. He had cancer.
"I am deeply saddened at the death of Bill Wilson," former First Lady Nancy Reagan said Saturday in a statement. "He was a dear friend for many years and a close advisor to my husband."
The businessman met Reagan and his wife at a dinner party in the early 1960s, when the future politician was first and foremost an actor. Wilson was a member of the inner circle of wealthy advisors who persuaded Reagan to run for California governor in 1966, then helped guide his political campaigns.
Wilson made his name as a manufacturer of oil-drilling equipment, a cattle rancher, a real estate developer and a savvy investor.
Along with William French Smith and Justin Dart, Wilson oversaw the trust put into place to manage Reagan's financial affairs once Reagan took public office, to avoid conflicts of interest.
In 1981, soon after Reagan was sworn in as president, he named Wilson, a Catholic convert and regular churchgoer, as his personal envoy to the Vatican. The United States had not had formal diplomatic relations with the Holy See since 1867, when Congress repealed funds for the consular post, citing a need to separate church and state.
Based on his admiration for Pope John Paul II and their shared commitment to eradicating communism in Eastern Europe, Reagan aimed to restore the United States' diplomatic ties. In 1984, the U.S. reestablished official relations, joining 107 other nations that recognized the Vatican as a sovereign body and the pope as an international statesman. Every president since Reagan has appointed an ambassador to the Vatican.
Wilson was elevated from personal envoy to full ambassador, but several missteps caused problems with the State Department.
He was reprimanded for what diplomats considered improper contact with Marc Rich, a commodities trader who fled to Switzerland to avoid being prosecuted for racketeering, fraud and tax evasion, as well as with Archbishop Paul C. Marcinkus, head of the Vatican bank when it became caught in a major financial scandal.
But his ultimate undoing came in 1986. Wilson had flown to Libya for an unauthorized secret meeting with Moammar Kadafi in January, only days after terror attacks at airports in Vienna and Rome had killed 20 people, the New York Times reported. U.S. officials believed Libya, then a major sponsor of international terrorism, to be responsible for the attacks and had urged the international community to isolate Kadafi, the mercurial leader of the north African nation.
Secretary of State George P. Shultz called Wilson's dealings with Kadafi an "embarrassment," and the ambassador submitted his resignation.
Despite the setback, Wilson remained close to the Reagans.
It was a friendship forged on horseback. Wilson and his wife, Betty, owned a ranch in Sonora, Mexico, and another in Santa Barbara County where they hosted the Reagans and threw birthday parties for Nancy. When Reagan became president, he asked Wilson to find a plot of land near his in California, and the 688-acre site they chose became the Reagans' Western retreat known as Rancho del Cielo.
"They were both horse riders, and that was their bond," Reagan biographer Lou Cannon said Saturday. "Reagan liked that ranch, and I think that made him fonder of Wilson. Whenever he talked about the ranch, he would always tell you that Bill Wilson found it, and he appreciated that."
William Albert Wilson was born in Los Angeles on Nov. 3, 1914, to William Webster Wilson and his wife, Ada. He attended Stanford University, where he met his future wife, Elizabeth "Betty" Johnson, the daughter of Pennzoil co-founder Luther Johnson. They married in 1938, he converted to her faith, and the couple had two children. She died in 1996.
Wilson earned a master's degree in mechanical engineering at Stanford and during World War II served as a captain in the Army Ordnance Corps. He worked for his father at Web Wilson Oil Tools, becoming president of the company before it was sold in 1960.
He later served as a director for the Earle M. Jorgensen Co., a Southern California steel distribution company run by another Reagan advisor, and Pennzoil Co., among others.
As governor, Reagan appointed Wilson to the board of regents of the University of California. Wilson also served on the board of trustees of St. John's Health Center in Santa Monica and Thomas Aquinas College in Santa Paula.
Besides his daughter Marcia of Los Angeles, Wilson is survived by another daughter, Anne Marie Wilson of Sonora, Mexico; six grandchildren; and 11 great-grandchildren.
Services are pending. His family suggests donations in his name to St. John’s Health Center or Thomas Aquinas College.