Active English regent involved in charge (9)
I believe the answer is:
energetic
'active' is the definition.
('energetic' can be similar in meaning to 'active')
'english regent involved in charge' is the wordplay.
'english' becomes 'e' (abbreviation).
'involved' is an anagram indicator (involved can mean confusing or complex).
'in charge' becomes 'ic'.
'regent' with letters rearranged gives 'nerget'.
'e'+'nerget'+'ic'='ENERGETIC'
(Other definitions for energetic that I've seen before include "Forceful and with great vitality" , "Lively, spirited" , "Vigorous and dynamic" , "Full of go" , "It's vital" .)