King to behave theatrically to get control (6)
I believe the answer is:
remote
'control' is the definition.
(remote control)
'king to behave theatrically' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'to behave theatrically' becomes 'emote' (I've seen this before).
'r'+'emote'='REMOTE'
'to get' is the link.
(Other definitions for remote that I've seen before include "device used by couch potato?" , "Far away as meteor (6)" , "Far-flung" , "Unlikely" , "in the middle of nowhere" .)