Learn English – the name of someone who was something before you

Doorman : http://en.wikipedia.org/wiki/Doorman

Words like forerunner, precursor, and predecessor may serve:
• forerunner, “a runner at the front or ahead”, also “a forebear, an ancestor, a predecessor” • precursor, “That which precurses, a forerunner, a predecessor, an indicator of approaching events”
• predecessor, “One who precedes; one who has preceded another in any state, position, office, etc.; one whom another follows or comes after, in any office or position”