'The US government': man's clue altered (5,3)
I believe the answer is:
uncle sam
'the us government' is the definition.
(I've seen this before)
'man's clue altered' is the wordplay.
'altered' indicates anagramming the letters.
'mans'+'clue'='mansclue'
'mansclue' is an anagram of 'UNCLE SAM'.
(Other definitions for uncle sam that I've seen before include "Statesman" , "Personification of the States" , "Cotton on" , "Federal government" , "Iconic male relative for America" .)