A person who criticises; someone who makes judgments or finds faults (British spelling).
From criticise plus -er suffix forming agent nouns. British English -ise form; American English equivalent is 'criticizer' with -ize.
The British/American spelling divide (-ise vs -ize) traces back to 17th-century printing conventions: French-influenced British printers preferred -ise while American printers adopted the more etymologically Greek -ize from science.
Complete word intelligence in one call. Free tier — 50 lookups/day.