what does it mean to be a core programmer?

I want to know what does the community refers to as a core programmer.

What should one do to be able to become a core programmer?

In other words, is it possible to do programming in a level in which one has knowledge of everything going on in the back end?

Is it possible to know everything under the hood while programming a software? If yes, with what language?

How can a programmer be independent of extra tools and rely firmly on his own knowledge?

Thanks