Paranoid old ruler putting Trotsky on trial briefly (7)

'paranoid old ruler' is the definition.
(character in Shakespeare's The Winter's Tale)

'trotsky on trial briefly' is the wordplay.
'trotsky' becomes 'leon' (I've seen this before).
'on' means one lot of letters go next to another.
'trial' becomes 'test' ('test' can be a synonym of 'trial').
'briefly' means to remove the last letter.
'test' with its final letter taken away is 'tes'.
'leon'+'tes'='LEONTES'

'putting' acts as a link.