To hear of (To be familiar with/to know the existence of/to recognise the name of
a person, thing or situation
usually famous in a particular field of entertainment, art or
profession
Examples:
Have you ever heard of a company called ABC Limited?
I’m surprised you’ve never heard of him; he’s quite well off.
Before we came to London, we had never heard of this type of crime.
To hear and To hear of, therefore, have different meanings and it is quite possible to hear of a musician without ever having heard him or her play.
* i.e. We never knew that this type of crime occurred.