Thaddeus James Dupper

Thaddeus “Thad” James Dupper, 68, of Castle Rock, Colorado, passed away peacefully at home on Saturday, June 7, 2025, after nearly two years of living with ALS. He was the devoted husband of Jean (Russell) Dupper for 24 years.

Born in Bay Ridge, Brooklyn, New York, Thad was the son of the late Melvin Alfred Dupper and Marion Elizabeth (Gotimer) Dupper, longtime residents of Brooklyn.

Thad is survived by his wife, Jean, and their two children: Andrew Russell Dupper and Katherine “Katie” Elizabeth Dupper of Castle Rock, CO. He is also survived by his siblings: Mark Andrew Dupper and his wife, Jane (Mannix), of Lake George, NY; Michael Alfred Dupper of Oxford, MS; and Maryeugene Dupper of Fern Park, FL. He leaves behind a nephew, Kieran Thomas Dupper and his wife Joan (Valentine) of South Glens Falls, NY, as well as several other nieces and nephews by marriage. Thad’s loyal golden retriever, Tucker, remained faithfully by his side and brought him great comfort and joy.

After retiring from a long and successful career in technology, Thad founded Dupper Analytics. There, he mentored high school and college students in business practices and coding—work that brought him deep satisfaction and purpose. Prior to that, he served as CEO of Secure64 in Greenwood Village, CO and earlier led Evolving Systems in Englewood, CO, as its CEO and Chairman of the Board.

He was committed to his community and served on the board of the Colorado Children’s Chorale and on the Finance Committee of the Archdiocese of Denver. A man of faith, Thad and his family were members of Pax Christi Catholic Church in Lone Tree.

Thad graduated from Xaverian High School in Brooklyn and went on to earn a Bachelor of Science in Computer Information Systems from Manhattan College (now Manhattan University) in 1979.

A lover of classic cars, Thad especially prized his 1966 Shelby Mustang. He also had a passion for woodworking and enjoyed building furniture—his proudest creations include handcrafted tables and cabinets. He also authored three novels, the first of which is based in Nantucket, MA where many of his fondest memories were made.

Above all, Thad’s greatest joy was his family. He cherished every moment with Jean, Andrew, and Katie, and his legacy of love, humor, and devotion will remain with them always.

A Funeral Mass will be held at 11 a.m. on Tuesday, June 24, at Pax Christi Catholic Church, 10675 Jaguar Drive, Lone Tree, CO 80124. A reception will follow at the church. All are welcome to attend.

In lieu of flowers, memorial donations may be made to the ALS Therapy Development Institute in Thad’s honor. (https://www.als.net/donate/)