I’ve been contributing to the English Wikipedia since 2005 (see my user page), and I’ve been an admin there since 2007. I’ve mostly edited articles on astronomy, local history and ships. I’ve also been contributing to Wikimedia Commons since 2006 (see my user page there) where I’ve uploaded over 2900 of my photographs.
I co-founded Wikimedia UK, the UK chapter of the Wikimedia Foundation, in 2008, and was a trustee of it between 2008 and 2013. Now a registered charity, this organisation helps support and promote free projects like Wikipedia. If you’re active on Wikipedia, then you should join!
I also co-invented the term ‘editathon’ (with Thomas Dalton). The first event under this term took place in January 2011 at the British Library. It has since spread world-wide!