That guy's rise in command should be celebrated (8)
I believe the answer is:
'celebrated' is the definition.
(historic can mean celebrated or important)
'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).
'should be' acts as a link.
(Other definitions for historic that I've seen before include "Connecting with old times" , "Significant" , "Landmark; famous" , "Choir sit (anag.)" , "Momentous, noteworthy" .)