I first met Dhog at a National Mathematics Summer School in Canberra in January 1986 - Catherine Playoust introduced us - and he was twice a member of Australia's Mathematical Olympiad team (in 1985 and 1986).
We went through uni together as undergraduates, we did honours in computer science together, and then as postgrad students shared a room (B24) in the Madsen basement along with Raf, Fred Curtis, Mitch, and others. Unlike some of us, David eventually finished his PhD. He appears in a photo of the traumasphere, one of Fred's most memorable origami constructions.
Dhog was always happy to help people - I often relied on him for C programming advice - though he did have a passion for doing things "the right way". He shared that with his friend John Mackin, who also died before his time, in 1996. Dave Watford and Geoff Bailey and I used to play bridge with Dhog and John, who insisted on playing a weird Tape Relay system he didn't understand himself but inflicted on Dhog anyway.
I screwed up one of the simulations I was running as part of my honours project, and filled up the entire honours disk with a huge file with the repeated line "Non-permanent edge colour". When my 21st birthday party came around, David gave me a present wrapped in a printout of (part of!) that file.
David and I had dinner together at least weekly, usually in Newtown: the Beirut Pizza Bar, Hard Nox and the Ban Thai have gone, but Efes and the Old Saigon are still there. And Wentworth hasn't gone anywhere.
I didn't stay in close touch with Dhog after he moved to the United States, working first for nCube and then for Bell Labs, but we caught up whenever he visited Australia.
The window manager I still use, and have used for the last decade, is 9wm, which Dhog wrote.