たる

たる is a classical, literary copula attached to a noun to express that the noun is in a certain role, status, or capacity. It gives a formal, slightly elevated or archaic flavor and is mostly found in written Japanese, historical texts, or stylistic narration. It is not used in everyday conversation. When you see たる after a noun, think of it as “in the role of …” or “as …” rather than the modern copula だ/です. It can occur after titles or professions (王たる者, 教師たる者) to describe someone who holds that position, or after a noun + の phrase to describe someone as that kind of person in that role. Be aware that the construction can sound formal or old-fashioned in modern contexts.