Classical character hoists troublesome lion (7)
I believe the answer is:
upsilon
'classical character' is the definition.
'upsilon' can be an answer for 'character' (I know that upsilon is a type of letter). I'm not certain of the 'classical' bit.
'hoists troublesome lion' is the wordplay.
'hoists' becomes 'ups' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'troublesome' indicates anagramming the letters.
'lion' anagrammed gives 'ilon'.
'ups'+'ilon'='UPSILON'
Can you help me to learn more?
(Other definitions for upsilon that I've seen before include "Greek 'u'" , "Greek letter" , "Character from abroad" , "Greek character" .)