Peter Francis Mueller, Sr. died peacefully in his sleep on April 12, 2021 at his home in Ridgefield, WA with his beloved wife of 20 years, Ellen (McLean) Mueller, by his side. He was 83 years old. Born in Roxbury MA on October 4, 1937, Peter was the youngest of Victor and Elizabeth Mueller's nine children. He received a BS in physics from Boston College and a MS in physics from Northeastern University. He also served in the U.S. Army and deployed to Germany during the Berlin Crisis. He married his high school sweetheart, Carol Ann (Haley) Mueller in August 1960. They made their home in Concord MA and together raised six children. They also lived in Westford and Orleans MA. Peter cared for Carol during her prolonged battle with cancer. Carol died in February 1996. Peter was a pioneering physicist, whose body of work grew to include more than 30 patents and dozens of articles published in technical journals. The impact of his inventions was far reaching and continues to benefit our nation today. While it was obvious that Peter loved the innovation and problem solving that his work involved, his family never knew exactly what he was working on, as his projects were usually classified. Peter's professional career included groundbreaking work in support of the Department of Defense at Technical Operations, Inc., Aerodyne Research, Inc., and Honeywell International, Inc., culminating in his co-founding of Innovative Imaging Systems, Inc. (IISI). Peter retired in 1997, remaining active as a member of IISI's board of directors. Peter was blessed to find love again when he met Ellen. They married in October 2000 and made their homes in Concord MA, Jupiter FL, Acton MA and most recently, Ridgefield WA. Ellen's loving care allowed Peter to spend his final years happily at home. Despite the ravages of twelve years of Alzheimer's, he remained cheerful, pleasant and loving to the very end. While Peter's career accomplishments were many, his most cherished legacies are his faith and his family. Peter was passionate about spiritual leadership, gardening, healthy eating and home renovations. He was known for his gentle humor, quick wit, ready smile and his kindness; he was a gentleman. Peter is survived by his wife, Ellen; her daughter and son-in-law, Annie & Marius Bilauca of Ridgefield WA; and his children: Peter & Betsy Mueller of Burlingame CA, Andrea & Jonathan Millard of Pittsburgh PA, Marie & Peter Klinkmueller of Acton MA, Eric & Rebekah Mueller of Needham MA, Gregory & Amy Mueller of Concord MA, and Kristin & Kevin Neprud of Wayland MA. He is also survived by his sixteen grandchildren, his brother James, and scores of nieces and nephews. He was predeceased by five brothers: Victor, Joseph, Robert, Francis and Frederick; two sisters, Elisabeth Ekstrom and Mary Hunt; and his stepson, Eric McLean Sproul. Family and friends will gather for visiting hours on Wednesday, April 21, 2021 from 5 to 7 pm at Dee Funeral Home, 27 Bedford Street, Concord Center. A private burial with military honors is planned for the following day at St. Bernard's Cemetery in Concord. Concord's Town Flag will fly at half-staff on Thursday, April 22, 2021 in recognition of Peter's military service to our country. In lieu of flowers, donations may be made in Peter's memory to The Alzheimer's Association . Arrangements are under the care of Dee Funeral Home & Cremation Service of Concord.