This word has nothing to do with a famous American songwriter nor with a carrier of coals, though it was once an occupation of sorts. Jonathan McColl told me about it. He had come across it on a death certificate dated 1885 as the occupation of a man of Dingwall in Scotland.
A colporteur was a pedlar who went from place to place selling printed materials such as books and newspapers. More specifically, he was employed by a religious society to distribute bibles and other religious tracts. Such men were the literal foot-soldiers of Christian missionary work. Even earlier were those encouraged by Martin Luther to distribute the religious writings of Protestant reformers. Such work could often be dangerous, as is shown by this decree from the Ottoman governor of Wallachia, in what is now Romania:
We order you to tear those writings that are against our Holy Religion. Whoever will seize and deliver up the publishers of those writings, shall receive 300 crowns. ... The Colporteur, on the contrary, shall be impaled alive upon the very place where he was seized.
Morning Post (London), 26 Apr. 1788.
In origin the word is French, from the verb colporter and is still current in both languages. It used to be thought that it came from col, neck, plus porter, to carry, implying somebody who conveyed his texts in a satchel across his chest. It’s now thought it’s an alteration of comporter, from the Latin comportare, to carry something with one.
It began to appear in English at the end of the eighteenth century and became widely used throughout the English-speaking world during the nineteenth, being taken by such organisations as the British and Foreign Bible Society wherever it operated. It fell out of favour at the end of the century and is now rather rare.