I was a bachelor student in Arren’s lab 3 years ago and I was going to start my PhD with him one week after he passed away. Since the day I have first met him, he has changed my life and I loved him like my own father. What I have experienced in the days since his death was absolutely astonishing. Colleagues and friends from all over the world sharing their experiences and admiration for Arren. Now, for me it was always difficult to judge, similar to how it is difficult for a flea to tell the difference between a lion and a cat, what great of a genius Arren was. The admiration and stories I have heard from people whose lives he has touched - students to professors - has reassured me that he was a one in a billion feline predator. I guess he would love this comparison. I vividly remember my first days when I started my thesis in his lab and me walking back to the station after my first day, excitedly calling my mum, telling her how happy I was and that I feel that I am exactly where I am supposed to be. Up to this day, I was more of a lazy student, doing only as much as I had to for getting good grades but rather focused on exploring Berlin’s nightlife. When I started to work with Arren, this attitude changed. He gave me a project that fascinated me and he believed in me from day one, constantly challenging me and pushing me to achieve better. Ultimately, I stopped seeing my bachelor thesis as work but instead as a vocation. But besides all his fascinating science… what an incredibly charismatic personality he had. Former drag queen, self-taught theologist, Magic the Gathering champion of Israel, history nerd, party animal, you name it. Everyone of my friends knows Arren at least from my stories of him because I am so fascinated by him. Naming his plate readers after drag queens with him being one of them, ringing his little brass bell when it was time for the legendary lunch breaks, wandering through the hallways and giving his workers funny nicknames. One day he walked into my laboratory calling me Kiddo. In retro perspective, it seems really foolish of me but that day I thought I could be extra smart and counter this new nickname with a naughty “yes daddy” as a response. Oh, was I wrong. What started off as a joke – him calling me Kiddo and me calling him Daddy – became a real thing. It even went that far that I introduced my real dad to him as my bio-daddy and Arren as my daddy to my dad. After my thesis, he tried to convince me to do some sort of fast track master and start my PhD right away in his lab. But I wanted to see the rest of the science world and thanks to his motivation, I felt capable enough to do my master’s at ETH, of course with his recommendation letter as my tailwind. When I left, I got a shirt which shows a circle with the stages of my academic career and marking my comeback to “Daddy” after my station at ETH. And this was also how it felt and which was my strong motivation since then. On my last day, I had a moment with him alone where we were laying in our arms, crying about me leaving the lab. But inside, I knew that I would come back to him. I left his group with incredible memories, colleagues, which became friends and of course completely unrealistic standards of academic research. But most importantly, I had found a mentor in him for my lifetime, how I hoped. During my time at ETH, we kept close contact. Whenever I visited Berlin, we met and played magic, whenever I had a tough decision to make, I would call him and ask for his advice or just check on him and reassure him that I would come back to him soon – he was always saying that I am taking too many turns and that I should rather hurry up to come back to him but I never understood his rush. I don’t know if he had a feeling that something like this could happen but I guess even in his death, he was right again, like always. After hearing the devastating news last week, like many other people in the world, my life is suffering from an existential crisis. Personally, what I really realized in the last days is how much I cared for Arren and that I did love Arren like my own father. Just like he had changed my life when I first met him, it feels like he has changed it again, just not for the good this time. With him, I lost a friend, mentor and father figure at once and right now my future without him feels hard to imagine and frightening. Besides looking at my chat and pictures with him, I catch myself going on his google scholar several times a day imagining what he could have achieved in the next 10 years if he was given more time. One thing which was clear to me: I would have followed him anywhere to keep on working with him and was excited to tickle him out of his grumpy shell and go partying with him in Tel Aviv. Well, I somehow have to say goodbye to these plans I had with him and try to look into the future. One thought which is giving me strength is that it is up to us to live out Arren’s heritage. Of course this also means to continue his ingenuine research ideas but more importantly to live how he has demonstrated how academia can be: Crazy, unconditionally supportive, collaborative, extravagant while never losing focus of performing rigorous science. I am sure it would make him happily rub his belly to see us living our lives and scientific careers sharing his vision. May he rest in peace. Love, your Kiddo Jan