Aha, I run riot, excitedly accepting thanks as a dictator! (13)
I believe the answer is:
authoritarian
'a dictator' is the definition.
('authoritarian' can be a synonym of 'dictator')
'aha i run riot excitedly accepting thanks' is the wordplay.
'excitedly' is an anagram indicator.
'accepting' means one lot of letters goes inside another.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'aha'+'i'+'run'+'riot'='ahairunriot'
'ahairunriot' anagrammed gives 'authoririan'.
'authoririan' going around 'ta' is 'AUTHORITARIAN'.
'as' is the link.
(Other definitions for authoritarian that I've seen before include "Enforcing strict obedience" , "Oppressively strict" , "Enforcing strict rules" , "Dictatorial" , "Domineering" .)