noun
A person or organization that provides support, often financial, political, or moral.
彼はそのプロジェクトの熱心な支援者だ。
He is an enthusiastic supporter of the project.
選挙では多くの支援者が集まった。
Many supporters gathered for the election.
後援者 is often used for formal backing, such as sponsorship or patronage, and can sound more official than 支援者.
Compound of 支援 (support) + 者 (person).