Persian ruler, former king, turned up trumps, ultimately (6)
I believe the answer is:
xerxes
'persian ruler' is the definition.
'xerxes' can be an answer for 'ruler' (I have seen 'Persian king' mean 'xerxes' so perhaps 'king' could also mean 'xerxes'). I'm unsure of the 'persian' bit.
'former king turned up trumps ultimately' is the wordplay.
'former' becomes 'ex'.
'king' becomes 'rex' (I've seen this before**).
'turned up' says the letters should be written backwards.
'ultimately' suggests the final letters.
The final letter of 'trumps' is 's'.
'ex'+'rex'='exrex'
'exrex' reversed gives 'xerxe'.
'xerxe'+'s'='XERXES'
Can you help me to learn more?
(Other definitions for xerxes that I've seen before include "Persian king, son of Darius (bridge of boats)" , "King of Persia, son of Darius" , "------I, son of Darius I, attempted invader of Greece, 480-79 BC" , "Name of ancient Persian kings" , "Ancient Persian king" .)