Former leader in Tehran has worked hard (4)
I believe the answer is:
shah
'former leader in tehran' is the definition.
I can't judge whether this definition defines the answer.
'has worked hard' is the wordplay.
'worked' is an anagram indicator.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'has' is an anagram of 'sha'.
'sha'+'h'='SHAH'
Can you help me to learn more?
(Other definitions for shah that I've seen before include "Former Persian ruler" , "Old Middle Eastern ruler" , "Persian emperor" , "Iranian emperor" , "Former hereditary monarch of Iran" .)