John Michael Brennan

John Michael Brennan, age 77, of Concord, passed away peacefully on January 18, 2026, after a brief illness. Mike was born on March 22, 1948, in Oakland. He spent his early years in Oakland with his mother, stepfather and sister, Patty, and later moved to Concord during his high school years to live with his father, stepmother, and his remaining siblings.
Following in his father's footsteps, Mike became a dental lab technician and, after many years of hard work and dedication, went on to establish his own business. His life was not without hardship—he struggled with alcoholism for many decades—but he found lasting recovery and had been proudly sober for 32 years at the time of his passing.
Mike's commitment to sobriety became one of the defining chapters of his life. He was deeply involved in Alcoholics Anonymous, sponsoring many members and forming countless friendships along the way. He was respected and admired for his unwavering dedication to helping others on their own paths to recovery.
Mike enjoyed spending time golfing and playing pool, and especially spending time with friends and family.
Mike married his first wife Susan Howland Brennan and they had their son Thomas Brennan Hashagen. Mike married his second wife Conchita Greenhouse Brennan who he had his remaining children with.
Above all, Mike loved his children and his grandchildren unconditionally and always tried to be there for them. His family was the center of his world.
Mike is survived by his five children: Thomas Hasahagen (Ulia), Alejandro Brennan (Francesca), Alicia (Brennan) Stockard, Carlos Brennan (Sindy), and Daniel Brennan; his two beloved granddaughters, Juliana and Autumn; and his five siblings: Patty (Baker) Harris, Charles John Brennan (Monica), Charleen Brennan Zube (Bob), Thomas "Jim" Brennan (Christy), and Sally Brennan Bone (Dave), and many nieces, nephews and cousins.
He was preceded in death by his mother and stepfather, Claire (Baker) Gibbons and George Baker, and his father and stepmother, Jack and Joan Brennan.
Mike will be deeply missed by his family, friends, and the many people whose lives he touched.
A Celebration of Life will be held Feb 22, 2026, at the First Street Ale House in Livermore from 12-3 pm. In lieu of flowers, donations in Mike's memory may be made to Alcoholics Anonymous.