We mourn the passing of one of the founders of our field. John Sulston was personally responsible for establishing the use of C. elegans to study development – with his stunning determination of the entire embryonic cell lineage by direct observation – as well as obtaining a complete genome sequence. He was a mentor and role model for many of us in the field who had the opportunity to work with him or know him personally, and an inspiration for many others who only knew him through papers and oral history. He demonstrated that comprehensive and careful description can lead to fundamental, mechanistic insights into biology and genomes. John also exemplified being collegial, community-minded, intellectually rigorous, scientifically intense and personally friendly.