Who didn't? Depending on exactly how you interpret the notion of "inventing backpropagation" it's been invented, forgotten, re-invented, forgotten again, re-re-invented, etc, about 7 or 8 times. And no, I don't have specific citations in front of me, but I will say that a lot of interesting bits about the history of the development of neural networks (including backpropagation) can be found in the book Talking Nets: An Oral History of Neural Networks[1].

[1]: https://www.amazon.com/Talking-Nets-History-Neural-Networks/...

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.

[1]: https://www.amazon.com/Talking-Nets-History-Neural-Networks/...