Seppo Linnainmaa, first publisher of "reverse mode of automatic differentiation to efficiently compute the derivative of a differentiable composite function that can be represented as a graph, by recursively applying the chain rule to the building blocks of the function" [1] aka backpropagation. Gerardi Ostrowski was first apparently but didn't publish.
Paul Werbos, "first described the process of training artificial neural networks through backpropagation of errors" [2].
Paul Werbos, "first described the process of training artificial neural networks through backpropagation of errors" [2].
[1] https://en.wikipedia.org/wiki/Seppo_Linnainmaa
[2] https://en.wikipedia.org/wiki/Paul_Werbos