Gunter Stein was a leading authority in control systems and theory, serving as a long‑time adjunct professor at MIT and spending over five decades at Honeywell Labs. He passed away on July 11, 2026, in his home state of Minnesota at the age of 84.\ \ Born in Germany, Stein emigrated to the United States as a child. His father worked as a tool and die maker at Fisher Body Works. Stein earned a B.S. from the General Motors Institute (now Kettering University) and an M.S. (1966) and Ph.D. (1969) in electrical engineering from Purdue University.\ \ At Honeywell, Stein led the development of navigation and control systems for aircraft flight controls, spacecraft altitude and orbit control, launch boosters, re‑entry vehicles, ship positioning, torpedo engines, autopilots, and precision‑guided weapons. His “most conservative” submission for the NASA F‑8 control contract became the only system successfully flight‑tested, establishing his reputation for rigorous problem solving.\ \ In 1977, MIT’s Laboratory for Information and Decision Systems (LIDS) director Michael Athans invited Stein to join as an adjunct. Stein taught one week per month in the EECS department, advised graduate students, read Ph.D. theses, and acted as a principal investigator. This arrangement lasted thirty years and profoundly shaped MIT’s approach to control theory.\ \ Colleague Munther Dahleh recalled that Stein could see through the mathematics to what truly mattered for applications. Nils R. Sandell noted that Stein helped shift the field’s emphasis from optimal control to robust control, especially in applying classical frequency‑domain techniques to single‑input‑single‑output systems with model uncertainty.\ \ Stein contributed to the B‑2 bomber, the F‑47 aircraft, and served for many years on the U.S. Air Force Scientific Advisory Board. In his influential 2003 Bode Lecture, “Respect the Unstable,” he warned that failures in automatic control—whether in nuclear reactors, aircraft, or spacecraft—can have catastrophic consequences and that engineers must teach the subject’s principles clearly, not hide behind mathematics. The lecture remains one of the most‑cited Bode talks.\ \ He was elected IEEE Fellow in 1985, received the first IEEE Control Systems Society Hendrik Bode Prize in 1989, was elected to the National Academy of Engineering in 1994, and won the IFAC Nathaniel Nichols Prize in 1999. Peers consistently described him as a warm, sociable, and deeply conscientious giant of the field.\ \ Beyond academia, Stein was an avid sailor and outdoorsman, exploring Minnesota’s lakes and forests. Memorial donations may be made to the Minnesota Nature Conservancy.\ \ Review: Stein’s rigorous engineering mindset and profound insight into robust multivariable control propelled modern aerospace and automation systems forward. His blend of industrial practice and academic mentorship left an indelible legacy.