#1 Alfredo di Stefano
Alfredo di Stefano was the OG, the Original Galactico.
Having successfully outmuscled Barcelona out of the deal (still the greatest transfer hijacking of all time) Santiago Bernabeu's Real Madrid would go on to build a footballing dynasty around the inimitable footballing talent and larger-than-life persona of the great Argentine forward.
A goalscorer-cum-playmaker extraordinaire, Di Stefano helped Madrid through their single most successful period - winning 5 European Cups and 8 League titles in the span of a decade... while helping them play the kind of swashbuckling, attacking football that Madrid fans (and even neutrals for that matter) have come to take for granted as part and parcel of the Madrid Way.
In terms of what he did on the field, and how much he helped shape the Real Madrid brand (both on and off the pitch), Real Madrid have never seen someone quite as influential as Alfredo di Stefano