The Sheriff (spoilers)

Actually, Pauline wasn't the only person who paid Silence to kill people (in fact, Pauline never paid him the $1000. Pollygut wanted her to sleep with him in exchange for the money, which she was not willing to do. So she basically said that Silence could have her instead of the $1000.)
The outlaws up in the mountains had paid Silence to kill the bounty hunters who were after him. The old woman, (mother of the young man that is killed by the bounty hunter with Loco at the beginning, posing as lawyers--sorry I don't remember his name) gives Silence her son's horse as payment to kill the bounty hunter who killed him, saying it's the only thing she has to pay him with.
I got the impression that was just what Silence did. He went around killing people for money (mostly bounty hunters, since they had killed his parents and made him mute). What supposedly distinguished him from the bounty hunters was that he was more ethical in deciding who to kill. The old woman says something to the effect of 'I know you, and that you fight for the weak against injustice.' Even Loco says 'He's trying to build a better world by/using his gun.' (At least he does in the Italian version. I know the dialogue is a little different in the English.)
I think the ending does suggest that Silence was actually quite noble. He must have suspected that Loco would cheat somehow (never mind that he was already badly hurt) but he went anyway, because he had to try to save all those people. You could argue that he was just particularly dumb and actually thought Loco would give him a fair fight, but I can't think of anything that suggests he was stupid.
I do think the Sheriff was a particularly noble character, though. He could have just sat back and stayed out of all this stuff that was going on, but he took his job seriously, which is why Loco killed him.

The most noble character, yeah. But I wouldn’t say the only noble character. Silence was noble too, the way he didn’t kill unless the other person drew first. And Silence walked into his death in an attempt to save people, no?