Before his passing on July 11, Susumu Tonegawa had served as a MIT professor for over four decades. At the memorial service on October 16, family, colleagues, mentees and friends spanning the whole arc of his MIT career gathered to celebrate not only his scientific achievements but, more importantly, his humanity. Sixteen speakers together painted a portrait of a man who demanded excellence while consistently showing kindness and a joyous enthusiasm for science (as well as art and baseball).\ \ Although he was a 1987 Nobel laureate for his breakthrough immunology work and is famed for pioneering memory research, the tributes focused little on awards and more on his personal impact. Picower Institute founder and director Myriam Heiman recalled that she first encountered his work as an undergraduate at Princeton, studying antibody diversity in an immunology class while reading Proust, feeling the intertwining of memory and art.\ \ Biology department chair Amy Keating praised Tonegawa’s passion for molecular biology as a model for students. She noted his bold move across the Pacific in the 1960s to pursue graduate studies in San Diego, learning a nascent field from scratch, and later applying molecular tools to both immunology and neuroscience despite the doubts he and his 1968‑class peers had about the field’s future.\ \ Former graduate student Arvind Govindarajan (now at McKinsey) joined Tonegawa’s lab in 1999 driven by curiosity about the brain rather than prior neuroscience training. Tonegawa encouraged him, “It is irrelevant what you know. What matters is what you want to work on,” and insisted that “if the problem is interesting, go forth and do it, but when you publish, it has to be perfect.” Another early mentee, Tom McHugh, quoted Tonegawa: “A journal doesn’t make your paper good, your paper makes the journal good,” and reminded everyone of the Japanese proverb “after victory, tighten your helmet.”\ \ 1980s mentee Juan Lafaille observed that Tonegawa was at least as demanding of himself as he was of his students. Post‑doc Tomás Ryan, now running his own lab at Trinity College Dublin, listed seven lessons he inherited from Tonegawa and said, “In Ireland we often say, you should never meet your heroes, you’ll only be disappointed. For me, the exception was Susumu … I was incredibly fortunate to have Susumu as a mentor.”\ \ As a community builder, Tonegawa founded the Picower Institute. MIT School of Science dean Nergis Mavalvala praised his vision that extended beyond his own science, creating a neuroscience community whose influence reaches far beyond his work on how memories are stored, recalled, and linked to emotion. Today the institute hosts 16 labs, about 400 people, and has trained hundreds more over the decades. Matt Wilson, the first professor hired for the Center for Learning and Memory, recalled Tonegawa’s absolute confidence in the success of the new Building 46, even before any renovation began. Govindarajan noted Tonegawa’s hands‑on involvement in the building’s design, working with architect Charles Correa to optimize every lab space.\ \ MIT Corporation member Barrie Zesiger recounted a story of Tonegawa standing at a huge window overlooking the train tracks beneath the new building, marveling at the minimal vibration – “like a child, the joy on his face.”\ \ Picower professor Li‑Huei Tsai described him as “unfailingly honest, warm, supportive, and never losing his sense of wonder.” Long‑time lab member Michele Pignatelli, upon learning of Tonegawa’s death, moved from heartbreak to “overwhelming gratitude,” saying, “Working with Susumu has been the greatest honor of my life. We will keep the flame burning.”\ \ Peter Mombaerts, a former immunology graduate student now directing a Max Planck neurogenetics unit, briefly mentioned the Nobel Prize only to stress that Tonegawa never suffered from “Nobelitis.” In a poignant anecdote, post‑doc Quentin Ferry shared how Tonegawa played joyfully with his young daughter, who has disabilities, at a lab cook‑out, seeing her simply as a child who wanted to play. “We will all remember Susumu’s brilliance. What I wish is that we also carry forward his kindness.”\ \ During the service, Picower director Myriam Heiman announced a generous $100,000 pledge to launch the Susumu Tonegawa Memorial Fund, an endowment to support curiosity‑driven research at the institute. Additional gifts are welcomed to grow the fund and ensure Tonegawa’s spirit of discovery continues to inspire future generations. Contributions can be made online or via email to memorial‑gifts‑office@mit.edu.\ \ Review: Tonegawa’s legacy transcends his scientific breakthroughs; it lies in the compassionate, community‑building ethos he embodied. That blend of rigor and humanity will continue to motivate the next generation of researchers.