Roman general, an old man, assuming control (7)
I believe the answer is:
agrippa
'roman general' is the definition.
(Marcus Vipsanius Agrippa, Roman general)
'an old man assuming control' is the wordplay.
'an' becomes 'a'.
'old man' becomes 'pa' (both can mean someone's father).
'assuming' is an insertion indicator (inserted letters are taken in or assumed).
'control' becomes 'grip' (grip is a kind of control).
'a'+'pa'='apa'
'apa' going around 'grip' is 'AGRIPPA'.
(Other definitions for agrippa that I've seen before include "Roman leader" , "Acts reported of this king" , "10 [GENERAL]" , "Powerful Roman" , "Marcus -, Roman fleet commander who defeated Cleopatra at Actium" .)