There isn't a person named "Hayvenhurst" – but there is a "Hay." Bill Robertson, director of L.A.'s Bureau of Street Services, says Hayvenhurst Avenue and Hayvenhurst mansion are named for the same man.
"Hayvenhurst was the estate of Encino subdivider William Hamilton Hay."
William Hamilton was better known as realtor "Billy Hay." He drew the streets and carved out the subdivisions in the early days of Encino. In the 1970s, a musical family moved from Gary, Indiana to Encino, bought a mansion on a five-acre lot, and called it Hayvenhurst.
The Jackson children, including Michael and Janet, grew up there. A replica of Michael's star on the Hollywood Walk of Fame is outside the front door. His parents still live in the house. Papa Joe Jackson has started a clothing company called Hayvenhurst, further spreading the fame of that early Encino real estate tycoon.