Who are the Regional Bell Operating Companies (RBOCs)?

There were originally 7 RBOCs.  Today there are only 3:

The original 7 RBOCs were formed from the 1984 breakup of AT&T.  AT&T originally consisted of 22 Bell Operating Companies (BOCs).  The 1984 Divestiture merged the 22 BOCs into 7 RBOCs: