Biff wrote...
Not a whole lot of detail to go on.

A1 = some string
B1 = some formula using LEFT that returns a portion of the string in A1
C1 = formula to return the rest of the string:

=SUBSTITUTE(A1,B1,"")

Safer to make that

=SUBSTITUTE(A1,B1,"",1)

in case the B1 formula were something like

=LEFT(A1,FIND(" ",A1)-1)

and A1 were something like

Robert Robertson