Old revolutionary’s name put up by king before once (8)

'old revolutionary's' is the definition.
(Russian revolutionary Alexander Kerensky)

'name put up by king before once' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'put up' becomes 'sky' (informal term meaning to throw something skyward).
'by' means one lot of letters go next to another.
'king' becomes 'k' (abbreviation for king in chess).
'before once' becomes 'ere' (archaic word for 'before').
'n'+'sky'='nsky'
'k'+'ere'='kere'
'nsky' put after 'kere' is 'KERENSKY'.