Alexander Rudensky’s research has defined regulatory T cells and the roles they play in autoimmunity, tolerance, allergies, infections, and cancer. After completing his PhD in Moscow in the early 1980s, Rudensky moved to the United States to study T cells under the mentorship of Charles Janeway. He is currently a professor of immunology at the Memorial Sloan Kettering Cancer Center. JCI Editor at Large Ushma Neill interviews Dr. Rudensky about his childhood in the Soviet Union and his early interest in mathematics and science. He discusses the mentors and coworkers who have shaped his research interests over time, and speculates about the immunological discoveries we can expect in years to come.