The term bagman (or bag man) has different meanings in different countries. "Bagman" is a term for a traveling salesman, mainly a British usage. The first known use of the term occurred in 1808. It can also mean a tramp or homeless man.
Bagman is also used just to mean assistant in military or police contexts as seen in the series Endeavour. Though it connotes someone who carries a bag of money, the term may also apply to a person who performs other small tasks, such as the personal aide to the US President.
It can mean a person who is a political fundraiser or is responsible for the financial side of a political campaign, the person who solicits donations. In part this has also led to the meaning of a person who solicits bribes for a public official.  It can be a person or paymaster designated to collect or distribute illicitly gained money ("dirty money"), such as bribes, or money that is collected in a criminal enterprise, such as a "protection racket" or in the running of a numbers racket. A bagman may also act as an intermediary in such transactions. A bagman may also be known as a delivery boy or running man, and he may receive a fraction of the money collected.