Emperor is to keep sleeping, interrupted by lion (8)
I believe the answer is:
napoleon
'emperor' is the definition.
(I know this)
'keep sleeping interrupted by lion' is the wordplay.
'keep sleeping' becomes 'nap on' (carry on napping).
'interrupted by' is an insertion indicator.
'lion' becomes 'leo' ('lion' in Latin).
'napon' placed around 'leo' is 'NAPOLEON'.
'is to' is the link.
(Other definitions for napoleon that I've seen before include "A pig farmer was chased by" , "Gold twenty franc piece" , "Solo, perhaps" , "leader in France, once" , "Former French gold coin" .)