Gonzalo ("Gon") Saenz Leon, died peacefully at home, aged 92, on March 3, 2022, in the company of family. Gon is survived by four of his five children, Renata (Leon) Davidson, Lydia Leon, Alec Leon, and Michael Leon; their partners and spouses, as well as five grandchildren and two great-grandchildren; and a large extended family. He is predeceased by his wife, Holly (Forbes) Leon, and first-born daughter, Paula (Leon) Roberts. Gon was born on April 26, 1929, in Madrid, Spain. His parents, Carmen Saenz de Vera and Francisco Leon Trejo, and he and his four older brothers, were exiled during the Spanish Civil War and settled in New York City in 1939. Gon attended the Putney School in Vermont, graduating in 1947. The Putney School is where he met his future wife, Holly, to whom he remained married for 69 years, until her death in 2019. He served as a trustee for the Putney School from 1959-1975. From 1947-1949, Gon attended Wesleyan University before transferring to Columbia University, where he graduated with a BA in 1951. He matriculated at the Columbia School of Engineering and was awarded a BS/MS in 1952. In 1953, he and Holly moved to Glastonbury, CT, where he started his career as an engineer at Pratt & Whitney Aircraft. In 1958, he embarked on a doctorate program at MIT, earning an ScD in 1963 in mechanical engineering. He was a faculty member in MIT's Department of Mechanical Engineering from 1960-64. After leaving MIT, Gon worked with Cahoon & Heasley, an engineering consulting firm in Cambridge, MA, and was an adjunct professor at Tufts University. From 1974 to 1987, he worked at the Cabot Corporation, in R&D. There he was involved in the development of Cabosil and carbon black applications. A Cabot co-worker recollected: "I was the luckiest professional woman working in the 1970s… Gon mentored us… he was strong, kind, funny and very, very smart." During his professional life, he was awarded a number of patents, one of which was for a method for densifying powders, another for an inflatable insulating material. After retirement from Cabot, he continued to work as an independent engineering consultant. Gon and Holly were married in 1950. They had five children between 1953 and 1960 and raised them in Sudbury, MA, where he and Holly continued to live the rest of their lives. Gon and Holly shared a deep love of music, which enriched their life-long bond. They formed a madrigal group which, for many decades, met regularly to sing and socialize. In 1986, Gon was elected to the Tavern Club in Boston. There, he enjoyed the convivial gatherings for dinners and lectures. Over the years he took part in many musical and theatrical performances. Friends, acquaintances, and fellow Tavern Club members describe Gon as a charming and a lively conversationalist. He loved the outdoors, skiing in winter, and fishing and hunting at the family home on Naushon Island in other seasons. He felt a deep connection with the Elizabeth Islands and served two 3-year terms as Selectman for the Town of Gosnold. He was proud of his role in advocating for a conservation easement to protect the woods adjacent to their Sudbury home. Throughout his life, Gon was a voracious reader, with an inquisitive mind. He read widely about a broad range of subjects, perhaps most importantly, the Spanish Civil War, which had displaced his Leon family. In his later years, he developed a keen interest in dog cognition, expounding often on the extraordinary intelligence of dogs and their relationships to humans. He maintained close contacts with his extended Leon family on both sides of the Atlantic and returned numerous times to Spain over his adult lifetime. In his later years, he repeated many times, "the most important things in life are one's relationships with friends and family." Gon is survived by his devoted Australian Shepherd, Kim, whom he adored and held close until his last breath. A memorial service will be held at a later date. Arrangements are under the care of Dee Funeral Home & Cremation Service of Concord.