Forgery is as old as money itself: Forum Ancient Coins has a nice collection of ancient forgeries.

This one above is forgery of an Antoniniaus coin:

"However if his too is just the core of a plated ancient forgery, then it is not the early mint product that I was postulating, but just the work of an ancient forger that could easily be joining an obv. and a rev. derived from two different coins. Checking my cast of Gunner’s coin against Heather’s image, the two coins do appear to be from the same dies. Apart from stealing mint dies, counterfeiters sometimes manufactured transfer dies from official coins, which also allowed them to produce counterfeits in mint style. " - Curtis Clay

See more ancient forgeries: Link - Thanks Al!

The Portuguese Banknote Crisis was the world’s largest case of counterfeiting.

The complex plot was conceived by Alves dos Reis, a Portuguese criminal while he was jailed for illicit arms dealing and embezzlement during World War I. After his release from prison, Reis presented himself as an agent of the Bank of Portugal (which was essentially a private company at the time) with a mandate to negotiate a loan for the ailing Portuguese colony of Angola in Africa.

Reis and collaborators presented this loan as a secret project of the Bank of Portugal and conned the currency printer Waterlow and Sons Ltd. of London to print Portuguese banknotes, specific for Angola, to the tune of 300 million escudos or £3 million (at 1925 exchange rate).

Reis proceeded to launder the money, created his own banks, invested in stocks and currency markets - and even buying stocks in the Bank of Portugal to gain control of that bank so he could thwart investigations into his scheme!

In 1925, the whole scheme came to a screeching halt when a bank teller found bank notes with duplicated serial numbers. All in all, Reis had managed to launder money equivalent to nearly 1% of Portugal’s annual GDP at the time!

The scandal became public knowledge and sparked political and economic instability in Portugal - the following year, the government was toppled in a military coup.

And Alves dos Reis? He was sentenced to 20 years in prison, served his time, and died penniless afterwards.

Link: The Effects of the 1925 Portugese Bank Note Crisis [pdf], an article by Henry Wigan | Alves dos Reis [wiki]

Emanuel "Jim the Penman" Ninger. Emanuel Ninger is a counterfeiter, who drew by hand, various denominations of US banknotes in the late 1880s.

He worked for weeks at a time on each note, and this was profitable because at the time one of those notes was extremely valuable (about $2000 or $4000 in today’s dollars). He gained a following, as the invariably wealthy people that ended up with these banknotes tended to realise their worth as works of art.

He was apprehended by the United State Secret Service in 1896, after a banknote ended up in a small puddle at a bar. A none-too-amused bartender realised that the ink was staining and the note was not genuine. Ninger served six months, and was forced to pay a restitution of $1 (The rumour that the $1 was one of his own works is more than likely an urban legend). He disappeared and probably did not make more works, though the art community was holding out, hoping for more to be discovered. None ever were.

Link: Emanuel Ninger [wiki]