Wikipedia
The CharlieCard is a MIFARE-based, contactless, stored value smart card used for electronic ticketing as part of the Automated Fare Collection (AFC) system installed by the Massachusetts Bay Transportation Authority (MBTA) at its stations and on its vehicles. The CharlieCard was made available to the general public beginning December 4, 2006. The last metal token was sold on December 6, 2006, at Government Center station.
The CharlieCard is named after a fictional character in a folk music song often called " Charlie on the MTA", which concerns a man trapped forever on the Boston subway system (then known as the Metropolitan Transit Authority, or MTA) because he cannot pay the 5-cent surcharge required to leave the train. Since the card's introduction, the Charlie character has been used on a variety of MBTA signs, including construction and directional signage.