This is a very familiar emoji thanks to the many male heroes from Marvel (MCU) or DC Comics. It's cleverly used when talking about a specific character or complimenting a boyfriend or friend for being dependable.

It represents the traditional image of a hero, but these days it's also used to describe a hero who is kind or wise, going beyond just physical strength. It's also used in a fun way to describe yourself when you've been a reliable helper to someone.