This article introduces an unknown predecessor of Leontief who, at the very beginning of the last century, invented the idea of an input-output table as the basis for finding an economic equilibrium. He gave examples of 'technical coefficients', formulated the idea of a computing office, and was the first to apply Perron-Frobenius's theorems to such Leontief-type models in order to demonstrate the possibility of the existence of an economic equilibrium. As a Jesuit, Potron was largely influenced by the 'social doctrine of justice'. Consequently, he was mainly concerned with social justice and economic efficiency, problems of 'fairness', and the setting of 'fair prices' and 'fair wages'. As a graduate of the Ecole Polytechnique with a PhD in mathematics, he applied mathematics to economic analysis, without any training or knowledge of economic methods.