This is an asterisk.
It's used to indicate a qualifying statement that must be attached to some word or sentence.
For some reason, people seem to confuse it with this person.
This is Asterix.
He's a French cartoon character who knocks about in ancient Gaul (as France used to be called a while back).
He fights a constant series of battles against the Romans along with his various friends. And, because he's got access to a magic potion, he and his mates always win.
It's supposed to be funny but, having read one of the stories, I disagree.
As you can see, there's a world of difference between the two.
So, to recap:
Asterisk - a little star-like thing that sits above a word or statement that needs some form of later qualification.
Asterix - an ancient Gaul in cartoon form who is constantly engaged in less-than-funny capers with Roman soldiers.
It's obvious when you spot it.