poster boy
Concise Oxford English Dictionary © 2008 Oxford University Press:
poster boy (or poster girl or poster child)
▶noun N. Amer. a person or thing that epitomizes or represents a specified quality, cause, etc.: a walking poster boy for the virtues of clean living.
– origin from the use in print advertisements of good-looking young people and appealing children.
'poster boy' also found in these Oxford entries:
