My maternal grandfather was one, in Italy. Had his golden age in the early '70s, when numismatica and stamp-collecting were worth real money. He even got a personal letter from the Pope, thanking him for help in moving some special-edition Vatican-issued coins. But it's been a slow decline ever since, and the shop was closed after he retired. I knew him as a sort of old "Del Boy" character, but in his heyday he flashed some real bling - houses, big cars, and so on - some of which he even managed not to waste before passing.

Somewhere at my parents', I probably still have a bunch of early-80s albums with some not-particularly-rare Roman coins in them. Despite the gift, it was a hobby I really didn't care for, to his displeasure. Nowadays, I understand it's a very, very small game.

To punch it up a bit, it's anyone with an interest in collecting/preserving coins or currency. Doesn't have to be an expert or rare. Coin/paper money/exonumia (tokens, fantasy issues) collectering = Numismatics

Also, fun fact for anyone reading, you can buy true, ancient Roman/Greek coins for a few bucks. Nice silver examples from certain well known emperors are often <$50. Just go on vcoins or somewhere reputable.

See also philatelist, notaphilist, lepidopterist, coleopterist, dipterist, etc.