This is an incredibly difficult post to write. Michael Benjamin Cohen, an amazing student and person passed away this week in Berkeley. Below is the official MSR statement (where he spent the summer together with many friends) and some personal remembrance. Also this is a picture of one of the many many happy moments we had together this summer at MSR (with Yin Tat Lee too):

**MSR statement:**

The Microsoft Research family is shocked and deeply saddened by the tragic loss of our colleague and friend Michael Cohen. Michael was a brilliant mathematician and a rising star in his field. He spent this past summer with us as a Microsoft Research Fellow, doing what he loved most. Over the summer, he made sweeping progress in online learning and online algorithms, two fields he had just recently become acquainted with. In addition to solving five open problems in these areas, he continued his substantial progress on the *k*-server problem, one of the most celebrated and notoriously difficult challenges in the space of adaptive algorithms.

Michael was a truly exceptional individual. We will remember Michael for his infectious smile and his larger-than-life personality. We will never forget his unrelenting curiosity, his thirst for knowledge, and his deep love for mathematics and theoretical foundations of computing. We are stunned by his loss. We will hold onto our memories of Michael, and know that his ideas and scientific accomplishments will continue on as important advances.

We extend our most sincere condolences to Michael’s family and friends.

**Personal notes:**

I have known Michael for less than a year, but in that short time span he had a profound impact on me, like only a handful of people have had in my scientific life. I will always remember our first meeting, on October 26th 2016 at MIT. We were about to start lunch with a small group of graduate students and Michael entered the room, he (gently) interrupted the conversation and his first sentence to me was a question about mirror descent that I was not able to answer (we now know the answer, and as it turns out his question was pretty deep and the answer highly non-trivial). This is a typical Michael story, and I’m sure anyone who has interacted with him had similar experiences, where a seemingly innocuous question (at a perhaps inopportune time) turned out to be extremely deep and interesting.

Michael’s way of doing mathematics was truly remarkable. He was relentlessly searching for the right way to look at a problem, and he was never satisfied with a hacky explanation. As far as I know he never wrote anything on paper while doing research. I assume that if the calculations were too long to fit in his head then it was probably the wrong approach anyway. Doing research with him was an immense pleasure. He was always willing to share his new and original point of view on his current readings. He was also interested in a breadth of topics that is only matched by a tiny fraction of researchers in theoretical computer science. As James Lee shared in his comment on Luca’s blog, I too was feeling that all of this was just warm-up for him. I am incredibly sad to have lost a friend and a great collaborator, but I’m also sad that we will never see Michael’s next steps.

Beyond his mathematical gift he was also a kind and gentle human being. Perhaps it was not obvious to see at first sight with his exuberant personality, but he was compassionate and caring.

We truly lost one of the best. It is really hard to cope with the unfairness of these events. We will do our best to share Michael’s wonderful ideas with the world, and to make his scientific accomplishements live on. Needless to say my heart breaks for his family and all my thoughts are with them at this moment.