Ian Mueller supervised my preliminary essay on Plato's Laws and was -- due to his extensive knowledge of Marx and his love of philosophy, more generally -- a very valued and critical reader of my dissertation (on Newton, Hume and Adam Smith).
Ian was one of two people at The University of Chicago that I nominated for a graduate teaching award. He won it the same year, I believe, as his wife, Janel, a very distinguished scholar of Renaissance English literature. His graduate teaching style can be best described as follows: you take a canonical text. You go through it line by line with your students, eliciting from them the now standard/canonical (often very dull) reading (sometimes you assign that, too). You then carefully show with them how it cannot possibly be right. Then you draw attention to an exciting, non-standard reading. Just before the end of class you show it, too, has fatal objections. Class ends (like a Platonic dialogue) in aporia. Repeat exercise at next class. (As Eric Brown reminded me, sometimes he would go through many more flawed positions.)
I always though of Mueller's as the (contemporary) philosophers' philosopher introduction to Euclid (and Greek math more generally). His book is just full of subtle arguments and observation. Like most of the great commentaries on Euclid (with which Ian was very familiar) it is as informative about Euclid as it is about the state of play in philosophic reflection on mathematics of its own day. Ian's contribution to Kraut's Cambridge Companion to Plato I continue to re-read with pleasure. I am always annoyed by those who tried to treat Ian as a niche scholar of ancient math--I am convinced that his papers help unlock far wider issues in Ancient Greek thought (no surprise given the importance of mathematical thinking in their philosophy) and, given the centrality of Euclid to western 'scientific' thought, to our philosophic culture.
My qualifying paper on the Laws was a commentary, and (despite opposition by others in the department) he was very supportive of it. If it weren't for his encouragement I probably would have left the discipline. But after the whole ordeal he told me he doubted anybody would ever get Plato convincingly right, but that there was still much to learn from Plato reception, both in the Ancient world but also from later periods (something I take to heart in some of my Early Modern scholarship). I had chosen the commentary form without much reflection, but much later something dawned upon me. While I did not keep up with all of his recent scholarship or the translations of the commentators, which I suspect he viewed as a kind of service to the discipline, but -- more poetically -- as a way of rehabilitating the commentary tradition as a philosophic art. He will be missed.