David was, well. Clearly a genius. Before I worked with him I'd been in another part of the Cavendish, doing sysadmin work for theoretical physicists including a Nobel laureate. The year I worked with David was different - more concentrated learning than I'd ever previously had.
And David was opinionated. Our review meetings would involve him asking for three different new config options based on ideas he'd had, and I'd argue him down to these making sense as a combination but not individually, but also this then being duplicative of some existing options, so if we implemented this correctly I could actually remove a preference instead of adding three more. I probably learned more from that than the coding itself.
And David could absolutely be a dick. He was very invested in his students but he was hard on them, and it was sometimes quite gendered. Probably not worse than the average Cambridge PI of the era (and definitely better than some others I knew), but that's always something that's tainted my experience.
Shortly before his death there was what was effectively a pre-memorial - a number of his past students presented their work, there was a dinner, people had an opportunity to say goodbye. I was lucky enough that the timing worked out for an existing trip to Europe, and I had the opportunity to say goodbye.
David choosing to tie up loose ends before his untimely departure was absolutely his style, and every time his name comes up I remember the fucking dreadful Sun IPX with its 256 colour display I had to use in a terrible office with the worst fluorescents I've ever seen for the first couple of months after I started. Nostalgia is weird, and I wish he was still with us.