He is a supporter of the local politician.
このイベントは多くの後援者のおかげで実現した。
This event was made possible thanks to many sponsors.
後援者 emphasizes ongoing financial or organizational backing, whereas 恩人 focuses on the personal gratitude one feels toward the helper.
後援者 is a native Japanese term emphasizing moral or organizational backing, whereas スポンサー stresses financial support in exchange for advertising.
後援者 is a neutral, formal word for a supporter or backer, while 金蔵 has a more colloquial, sometimes slightly cynical tone of being used as a money source.
Compound of 後援 (こうえん, 'support, backing') and 者 (しゃ, 'person'). The term is a straightforward Sino-Japanese formation.