Remarkable, that guy's rise in command (8)
I believe the answer is:
historic
'remarkable' is the definition.
(I've seen this before)
'that guy's rise in command' is the wordplay.
'that guy's' becomes 'his' (belonging to a man).
'rise' becomes 'tor' (I've seen this before).
'in command' becomes 'ic' (military abbreviation).
'his'+'tor'+'ic'='HISTORIC'
(Other definitions for historic that I've seen before include "Of significance in the past" , "Momentous, noteworthy" , "remarkable" , "Significant" , "Memorable" .)