In my country (and I think by now most non-US developed countries do something similar) everybody has a CPR(CentralPersonRegistry) number that identifies you, you need it to do almost everything so you aren't likely to forget (its your birthday + 4 digits). You get it at birth or if you come to the country for more than 3 months, it legally mandatory and it's also legally required to inform the government if you change your address. Also, if you (ever) had a modern passport there is already a database with your fingerprints, face and iris scan in it.