When was the earliest appearance of Empirical Cumulative Distribution Plots? I would be surprised if we actually had a date here. I am curious who, if anyone, created the ecdf plot. When did the ecdf make its first appearance? If we do not know when the first ecdf plot was made do we at least have a general time period of when the started to show up?

It was in 1933.
According to M.A. Stephens, Kolmogorov first formalized the notion of empirical distribution function.
Additionally, according to D.A. Darling, it was originally used to define the Kolmogorov-Smirnov statistic, so it was in fact Empirical Cumulative Distribution Function.
Stephens, M.A. (1992). Introduction to Kolmogorov (1933) On the Empirical Determination of a Distribution. In: Kotz, S., Johnson, N.L. (eds) Breakthroughs in Statistics. Springer Series in Statistics. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-4380-9_9
Darling, D. A. The Kolmogorov-Smirnov, Cramer-von Mises Tests. The Annals of Mathematical Statistics, vol. 28, no. 4, 1957, pp. 823–38. JSTOR, http://www.jstor.org/stable/2237048. Accessed 15 Nov. 2022.
