Sonny is kind of a nickname for "son" - but Son could also be a nickname for Sonny. *mind blown*
Famous people named Sonny:
Electronic music producer Sonny Moore (a.k.a. Skrillex); boxer Sonny Liston; singer/U.S. Congressman Sonny Bono; baseball player Sonny Gray.
This name can also be a diminutive of the Italian names Salvatore and Santino.