Farmer, an Argentinian who fought between rivers (7)
I believe the answer is:
rancher
'farmer' is the definition.
(rancher is a kind of farmer)
'an argentinian who fought between rivers' is the wordplay.
'argentinian who fought' becomes 'Che' (revolutionary Che Guevara).
'between' indicates putting letters inside.
'rivers' becomes 'rr' (two abbreviations for river).
'an'+'che'='anche'
'anche' going inside 'rr' is 'RANCHER'.
(Other definitions for rancher that I've seen before include "US cattle farmer" , "US cattle breeder" , "Cattleman" , "Hacienda owner" , "Cattle farmer in the Americas" .)