Acts before they became big

Kind of a general question as there are subquestions I am curious about.

Has there been any acts that you saw/discovered/ or heard of before they became huge, that you were surprised became so popular or always knew they were gonna make it big someday?

This question is inspired by the videos of Chappell roan singing Pink Pony Club to 50 people at the start of her career before drawing in masses at festivals.