They are typically referred to as Porter Duff blend modes, so I assume that these algorithms were invented mainly by those guys. (by Thomas Porter and Tom Duff)
This set me on an interesting trail. I haven’t found anything yet that links Porter and Duff to the modern blend modes as we know them, but I did find this 1984 SIGGRAPH paper they authored that appears to have laid much of the groundwork! https://graphics.pixar.com/library/Compositing/paper.pdf
