c. 1500, "one who proclaims," agent noun from call (v.). Meaning "one who announces step changes at a dance" is short for caller-out (1882). Meaning "a social visitor" is attested from 1786; as "one who places a telephone call," 1880.
you need a fiddler and a caller for country dancing
the callers were mothers summoning their children home for dinner
who is the caller of this meeting?
there were so many callers that he finally disconnected the telephone
`caller' is a Scottish term as in `a caller breeze'