noun
A person who criticizes or finds fault, often in a systematic or principled way. Can be used for critics of government, art, ideas, etc.
彼は政府の政策の厳しい批判者だ。
He is a harsh critic of the government's policies.
その作家は社会の批判者として知られている。
The writer is known as a critic of society.
Compound of 批判 (criticism) + 者 (person). The exact historical derivation is straightforward; the word follows a common pattern for forming agent nouns.