Soap for a succession of rulers (7)
I believe the answer is:
dynasty
I believe this is a double definition.
'soap' is the first definition.
(I know that Dynasty is a soap)
'succession of rulers' is the second definition.
(eg a royal dynasty)
'for a' acts as a link.
(Other definitions for dynasty that I've seen before include "Line of kings" , "show" , "Ruling sequence" , "Succession of rulers from one family" , "Family line of rulers" .)