It is with a sadness shared by many of my scientific friends and colleagues that I learned of the passing of John Holland, who is in some sense, my intellectual grandfather. My PhD advisor, Dave Goldberg, was advised by John Holland, and it is in this line of unconventional scientific curiosity that I was lucky enough to be raised.I remember well, when I was an awkward graduate student at one of my first conferences, in the lunch hall at a table of strangers, all graduate students from better-named Universities, all having accents that had less regional baggage. I was clumsily attempting to tell them what I was doing with Genetic Algorithms (GAs) in my Master's Degree, when John, the father of GAs, walked up, put a friendly hand on my back, and complimented me on a recent paper. That made all the difference to my confidence that day, and ever since. John treated me as he did all others with scientific curiosity: as an equal colleague and friend, regardless of status or rank.John played a seminal role that extends well beyond the creation of a class of algorithms: he was key in creating a way of thinking about the world, what we now call Complex Systems Science: the study of systems that demonstrate behaviours that aren't well treated by reductive models. I feel that this way of thinking about the world is shifting the entire scientific endeavour in a way that will touch literally every human being's life in the coming millennia.John will be missed, but his intellectual and personal legacy, which helped train Dave, and then me, and so many others, will echo throughout time. RIP, John Holland.