When I was a grad student, one of my professors was A. A. Hill. Rumor had it that he was quite wealthy because his relatives had written this song and that he shared in the profits. I don't know if that was true, but it was interesting.
Now I Know: Happy Birthday (c): "The song is iconic. [. . . .]But unlike the second and third most recognizable English songs, 'Happy Birthday' has another distinction:
It is under copyright.
In 1893, two sisters from Kentucky, Mildred and Patty Hill, composed a song called 'Good Morning to All.' The lyrics -- 'Good morning to you / good morning to you / good morning dear children / good morning to all' -- are foreign to modern ears. But the melody they used for the song is now more commonly known for its use in 'Happy Birthday.'"