Fickle character, clumsy actor and English stars in vacuous cartoon (9)
I believe the answer is:
chameleon
'fickle character' is the definition.
(I know this)
'english stars in vacuous cartoon' is the wordplay.
'english' becomes 'hame' (I can't justify this - if you can you should give a lot more credence to this answer).
'stars' becomes 'leo' (constellation).
'in' is an insertion indicator.
'vacuous' suggests removing the centre.
'cartoon' with its middle removed is 'cn'.
'hame'+'leo'='hameleo'
'hameleo' put into 'cn' is 'CHAMELEON'.
'clumsy actor and' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for chameleon that I've seen before include "Ha! Clone me (anag)" , "fickle person" , "Variable-colour reptile" , "colour changer" , "One far from constant" .)