Jeroen is just this guy, you know. He's a veteran programmer who at one time found himself chin deep in webdev and decided the best thing for his sanity was to retire from it. Then Abner proposed what would become Handmade Network and he decided to dust off his keyboard and join the fray, only to find the keyboard wasn't particularly dusty yet. Some keys were getting stuck or unresponsive, sure, but a replacement keyboard soon fixed that. When not wrangling RSI, he develops the backend software that makes the website tick.
Apart from this he has a keen interest in low-level programming, optimisation, compiler writing and games development, among other subjects. When the site software is sufficiently mature, he plans to do an educational series on the Handmade Network, passing on some of the 30 years of collected knowledge he's gathered.