Initially a king; possibly raise to an emperor (6)
I believe the answer is:
kaiser
'to an emperor' is the definition.
(German term for emperor)
'initially a king possibly raise' is the wordplay.
'initially' says to take the initial letters.
'possibly' indicates an anagram.
The first letter of 'king' is 'k'.
'raise' anagrammed gives 'aiser'.
'k'+'aiser'='KAISER'
(Other definitions for kaiser that I've seen before include "Ruler over empire" , "Old German emperor, pre-Hitler" , "Old German emperor like Bill" , "Former German emperor" , "Emperor of Austria or Germany until 1918" .)