Janet was invented in 650 AD when a wandering druid needed a quick solution to the problem of converting stones into beer. He failed to patent his invention, however; a disaster for the druid (whom history must reluctantly consign to anonymity) but a blessing for entrepreneurial 'Saxon metal' bard Geoffrey Heafodbanger, who persuaded the druid to swap his invention for a magic bean. From Heafodbanger the secret of Janet was passed down from generation to generation, whispered from seventh son to seventh son, refined (though you mightn't guess it) and reconfigured, finally becoming the complicated mustelid maintenance process we now know.
Six feet tall, two inches wide, and made entirely of platinum except for a single thin strip of paper, today's Janet would be wholly unrecognisable by Geoffrey Heafodbanger; but any druid worth his mistletoe would sense the mythical continuity between his original invention and the modern methods.
History does not record what happened to the magic bean, though a certain family in Somerset are suspiciously reticent about the techniques by which they regularly sweep the board at village shows with their prodigious vegetables.