Who discovered Spearman's rank correlation?

Spearman's Rank Correlation coefficient rho is the one nonparametric measure of association to feature in most modern courses, textbooks and computer packages in elementary statistics. This paper covers the tortuous route to the present position over the period 1904 to the early 1950s, casting considerable doubt on the way as to the easy identification of any one person (including Spearman) with the coefficient.