researcher; scholar; student (of)
Refers to someone who studies or researches a particular field, often with a nuance of dedication or expertise. Can be used for both professional researchers and serious amateur scholars.
He is a Shakespeare scholar.
この分野の研究家として知られている。
He is known as a researcher in this field.
He is known as a researcher of Japanese yokai culture.
According to a researcher, this festival has a history of over a thousand years.