William Guggenheim III (March 2, 1939 - May 20, 2023) was a pioneer in the field of After-Death Communication (ADC) experiences. He is considered to be the "father of ADC research" and has written and spoken on this subject for more than 25 years.

Guggenheim was a native of Long Island, New York City, and New Jersey. During his first 35 years, he was a stockbroker and a securities analyst on Wall Street.

In the mid-1970s, Guggenheim began studying spiritual teachings. He studied for a year with the Reverend Anne Gehman, a psychic, medium, healer, and teacher, who helped him expand his concept of reality. In 1977, he attended a five-day "Life, Death, and Transition Workshop" with Dr. Elisabeth Kübler-Ross. It was at this workshop that he was exposed to experiences of after-death communication.

In 1988, he began researching after-death Communication (ADC). Not long after that, he and his former wife, Judy Guggenheim, founded The ADC Project to conduct the first in-depth research of After-Death Communications. During their seven years of research, they interviewed 2,000 people and collected more than 3,300 firsthand accounts from people who believed they had been contacted by a family member or friend who had died. They self-published 5,000 copies of Hello From Heaven! in October of 1995 and then got a contract with Bantam Books. Bantam Books published Hello From Heaven! in hardcover in April 1996. It was the first book published on the topic of after-death communication.

After Hello From Heaven! was published, Guggenheim spoke about after-death communications at numerous conferences and on television and radio shows.