recommender; nominator; referee
A person who formally recommends someone for a position, award, or admission. 推薦者 is the standard term; 推薦人 is also used in similar contexts.
A letter of recommendation from a recommender is required for graduate school applications.
He is listed as a nominator for the award.
A letter of recommendation, the document written by a 推薦者.
Compound of 推薦 (recommendation) + 者 (person). The reading follows standard on'yomi.