What is a person obsessed with a hobby or intellectual pursuit called?

The word geek is a slang term originally used to describe eccentric or non-mainstream people; in current use, the word typically connotes an expert or enthusiast or a person obsessed with a hobby or intellectual pursuit, with a general pejorative meaning of a "peculiar person, especially one who is perceived to be overly intellectual, unfashionable, boring, or socially awkward".

Some use the term self-referentially without malice or as a source of pride, often referring simply to "someone who is interested in a subject (usually intellectual or complex) for its own sake". Nonetheless, it remains a pejorative, widely used in an abusive manner especially against children and teens who may be more focused on studies, while less popular, fashionable, or socially inclined.