I think you'll find that backpropagation was essentially developed (multiple times) during the 60s in the field of control theory and first implemented in the early 70s.
Ed: To be clear, the idea to use them to adapt the weights of NNs was also from the 70s but only rediscovered and applied to MLPs by at least two independent groups/individuals in the 80s.
I think you'll find that backpropagation was essentially developed (multiple times) during the 60s in the field of control theory and first implemented in the early 70s.
Indeed. The book Talking Nets: An Oral History of Neural Networks[1] covers a lot of this ground. Read it and you'll see many people who were involved in the early history NN's mentioning how backprop was discovered and re-discovered over and over again.
Ed: To be clear, the idea to use them to adapt the weights of NNs was also from the 70s but only rediscovered and applied to MLPs by at least two independent groups/individuals in the 80s.