I mean, I think Kanye then Drake are the most significant influences on the folks who do it now.

Missy and Lauryn Hill and to a lesser extent Cee-Lo did it in their day, but for Missy and Lauryn it was also mixed up in sexism around rap and R&B.

In terms of blending it seamlessly with rapping, certainly Bone Thugs and Freestyle Fellowship.

There are a lot of tributaries. No doubt though that Kanye and Drake are the primary source of nearly everyone doing it now.