“[R]ecent revisions of an article can be peeled off to reveal older layers, which are still meaningful for historians. Even graffiti applied by vandals can by its sheer informality convey meaningful information, just like historians learned a lot from graffiti on walls of classic Pompei. Likewise view patterns can tell future historians a lot about what was hot and what wasn’t in our times. Reason why these raw view data are meant to be preserved for a long time.” Erik Zachte wrote these lines in a blog post <https://web.archive.org/web/20171018194720/http://infodisiac.com/blog/2009/07/michael-jackson/> almost ten years ago, and I cannot find better words to describe the gift he gave us. Erik retired <http://infodisiac.com/back_to_volunteer_mode.htm> this past Friday, leaving behind an immense legacy. I had the honor to work with him for several years, and I hosted this morning an intimate, tearful celebration of what Erik has represented for the Wikimedia movement. His Wikistats project <https://stats.wikimedia.org/>—with his signature pale yellow background we've known and loved since the mid 2000s <https://web.archive.org/web/20060412043240/https://stats.wikimedia.org/>—has been much more than an "analytics platform". It's been an individual attempt he initiated, and grew over time, to try and comprehend and make sense of the largest open collaboration project in human history, driven by curiosity and by an insatiable desire to serve data to the communities that most needed it. Through this project, Erik has created a live record of data describing the growth and reach of all Wikimedia communities, across languages and projects, putting multi-lingualism and smaller communities at the very center of his attention. He coined metrics such as "active editors" that defined the benchmark for volunteers, the Wikimedia Foundation, and the academic community to understand some of the growing pains and editor retention issues <https://web.archive.org/web/20110608214507/http://infodisiac.com/blog/2009/12/new-editors-are-joining-english-wikipedia-in-droves/> the movement has faced. He created countless reports—that predate by nearly a decade modern visualizations of online attention—to understand what Wikipedia traffic means in the context of current events like elections <https://web.archive.org/web/20160405055621/http://infodisiac.com/blog/2008/09/sarah-palin/> or public health crises <https://web.archive.org/web/20090708011216/http://infodisiac.com/blog/2009/05/h1n1-flu-or-new-flu-or/>. He has created countless <https://twitter.com/Infodisiac/status/1039244151953543169> visualizations <https://blog.wikimedia.org/2017/10/27/new-interactive-visualization-wikipedia/> that show the enormous gaps in local language content and representation that, as a movement, we face in our efforts to build an encyclopedia for and about everyone. He has also made extensive use of pie charts <https://web.archive.org/web/20141222073751/http://infodisiac.com/blog/wp-content/uploads/2008/10/piechartscorrected.png>, which—as friends—we are ready to turn a blind eye towards. Most importantly, the data Erik has brougth to life has been cited over 1,000 times <https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=stats.wikimedia.org> in the scholarly literature. If we gave credit to open data creators in the same way as we credit authors of scholarly papers, Erik would be one of the most influential authors in the field, and I don't think it is much of a stretch to say that the massive trove of data and metrics Erik has made available had a direct causal role in the birth and growth of the academic field of Wikimedia research, and more broadly, scholarship of online collaboration. Like I said this morning, Erik -- you have been not only an invaluable colleague and a steward for the movement, but also a very decent human being, and I am grateful we shared some of this journey together. Please join me in celebrating Erik on his well-deserved retirement, read his statement <http://infodisiac.com/back_to_volunteer_mode.htm> to learn what he's planning to do next, or check this lovely portrait <https://www.wired.com/2013/12/erik-zachte-wikistats/> Wired published a while back about "the Stats Master Making Sense of Wikipedia's Massive Data Trove". Dario -- *Dario Taraborelli *Director, Head of Research, Wikimedia Foundation research.wikimedia.org • nitens.org • @readermeter <http://twitter.com/readermeter>