porter (n.1)
"person who carries," late 14c. (mid-13c. as a surname), from Anglo-French portour, Old French porteor "porter, bearer; reporter" (12c.), from Late Latin portatorem (nominative portator) "carrier, one who carries," from past participle stem of Latin portare "to carry" (see port (n.1)).
porter (n.2)
"doorkeeper, janitor," mid-13c. (late 12c. as a surname), from Anglo-French portour, Old French portier "gatekeeper" (12c.), from Late Latin portarius "gatekeeper," from Latin porta "gate" (see port (n.2)).
porter (n.3)
type of dark beer, 1734, short for porter's ale (1721), from porter (n.1), because the beer was made for or preferred by porters and other laborers, being cheap and strong.