Clever swimmer Lundgren at home (7)
I believe the answer is:
dolphin
'clever swimmer' is the definition.
(dolphins are highly intelligent)
'lundgren at home' is the wordplay.
'lundgren' becomes 'dolph' (actor Dolph Lundgren).
'at home' becomes 'in' (similar in meaning).
'dolph'+'in'='DOLPHIN'
(Other definitions for dolphin that I've seen before include "Snall type of whale" , "Relative of whale" , "Sea mammal like large porpoise, friendly towards people" , "Intelligent marine mammal" , "Marine mammal with an elongated beak-like head" .)