Manco initially dislikes Mortimer, but later befriends him. Mortimer is portrayed by Lee Van Cleef, who also plays the villainous Angel Eyes in The Good, the Bad and the Ugly. If the trilogy is watched chronological order, (The Good, the Bad and the Ugly is a prequel.) then Manco's dislike of him makes a lot more sense, because his looks must've reminded him of Angel Eyes. note As the movies were not intended as a strict trilogy there may not be any need to speculate.
Indio has become a successful gunslinger in part because he's a rotten cheating bastard. Every single duel he initiates is done only after he's psychologically broken or tipped the scales in his favor.
Manco figures out that there's a gunslinger about to kill him in part because he counted out all the dead bounties in his cart and realized there was one missing.
