Most interesting case I've come across was a guy who just had one name. No surname or anything. He was once questioned by police (regarding a theft in the shop he worked in) and explained that his parents were "a bit weird". He was originally American, so apparently that's also a possibility there? And apparently the Dutch system allowed it, although the police seemed to struggle with it and may have duplicated his name.
It can go the other extreme too of course: https://www.stuff.co.nz/nz-news/360848808/worlds-longest-nam...