1.  postulator(n = noun.person) - (Roman Catholic Church) someone who proposes or pleads for a candidate for beatification or canonization;

2.  postulator(n = noun.person) - someone who assumes or takes something for granted as the basis of an argument;
Derived form verb postulate₂

postulator, n.
1 a person who postulates.
2 RC Ch. a person who presents a case for canonization or beatification.