Oliver Twist is the protagonist, and Fagin is the villain. People seem to be affected by Oliver in that he brings out the best in them. Oliver is a virtuous and innocent young boy. Fagin tries to corrupt him as he has all of the other boys.
Fagin seems polite, but he only treats the boys well when they give him something in return.
The Jew grinned; and, making a low obeisance to Oliver, took him by the hand, and hoped he should have the honour of his intimate acquaintance. (ch 8, p. 39)
Oliver affects Fagin because he ultimately brings out his downfall, but Fagin does not really repent. He is a greedy, sinful man.
There are other characters that are affected by Oliver. Oliver seems to make quite an impression on Dodger and Nancy. Both of them do seem to care about him, in their way. Nancy does not feel that Fagin’s place is appropriate for Oliver. Nancy risks a beating to avoid going to kidnap Oliver back. She also tries to protect Oliver from Sikes and Fagin.
'I don't care for that, Bill, I don't care for that,' screamed the girl, struggling violently with the man, 'the child shan't be torn down by the dog, unless you kill me first.' (ch 16, p. 78)
Oliver’s goodness, rather than Fagin’s “badness,” is able to turn Nancy good, but she pays with it for her life. She sneaks out to help Oliver, and Sikes finds out and kills her.