He made a large fortune for his day with his songs and was a popular idol.
"Let us come now to the gravamen of my complaint.

You charge on the authority of mere gossip from the late Will S.Hays, that Foster did not compose his own music, but that he had obtained a collection of unpublished manuscripts by an unnamed old 'German musician and thus dishonestly, by pilfering and suppression' palmed off upon the public themes and compositions which he could not himself have originated.
Something like this has been said about every composer and writer, big and little, whose personality and habits did not impress his immediate neighbors as implying the possession of genius.

The world usually expects direct inheritance and a theatric impressiveness of genius in its next-door neighbor before it accepts the proof of his works alone.
For that reason Napoleon's paternity in Corsica was ascribed to General Maboeuf, and Henry Clay's in early Kentucky to Patrick Henry.

That legend of the 'poor, unknown German musician' who composed in poverty and secrecy the deathless songs that have obsessed the world of music lovers, has been told of numberless young composers on their way to fame, but died out in the blaze of their later work.

I have no doubt they told it of Foster, as they did also of Hays.