noun
Neutral term for a person who believes in a religion, doctrine, or person. Often used in religious contexts, but can also refer to loyal followers of a philosophy or leader.
彼は熱心な仏教の信者です。
He is a devout Buddhist believer.
その
That politician has many followers.
noun
Colloquial, often slightly derogatory term for an obsessive fan of a celebrity, brand, or product. Implies uncritical devotion.
彼はアップルの信者で、新製品が出るたびに買っている。
He's an Apple fanboy and buys every new product they release.
あのアイドルの信者はコンサートに必ず来る。
That idol's superfans always come to her concerts.