the first person to do something, or the first thing to happen:
There are now many similar housing projects but this was the first.
We hope this year's festival will be the first of many.
the first to do something
I always thought my sister would be the first to get married.
James was the first to arrive.
used when you have just discovered something that other people already know, and you are slightly annoyed:
The first I knew he was in York was when I got an email from him.
the first I knew/heard of/about
The first I knew about it was when Tony called me.
used after the name of a king, queen, or Pope when other later ones have the same name:
Queen Elizabeth the First (=written as Queen Elizabeth I)