Role in the film
Bill Sikes is first seen entering Fagin's warehouse with his girlfriend, Nancy and his dog, Bull's Eye to discuss business with Fagin and to get paid for a job he did last Sunday (probably a theft or a murder). However, Fagin has been known to cheat Sikes for years and make excuses for not paying him, which later leads to Sikes threatening him with his life unless he gets paid, which Fagin does without further hesitation.
After Nancy meets and takes a sudden liking to Oliver, an orphaned boy found on the streets by Dodger and taken in by Fagin, Sikes calls for her to attend further business with Fagin. So, Fagin tells his thieving boys to get outside and do their jobs; not before instructing Dodger to keep an eye on Oliver and make sure nothing happens to him.
A few days later, after Oliver gets accidentally caught by the police on his first day on the job as a thief (job which Dodger managed to succeed instead), Sikes gets very upset and worried thinking that Oliver might betray them and have them sentenced to death even if Nancy tries to calm him down by telling him to let Oliver live a new life with the people who bailed him out and took him in their home. His complaints lead to an argument between him, Fagin, Nancy, and Dodger since they know that Oliver is not the kind of boy to turn traitor on them. Then, Sikes threatens to hurt Dodger for letting Oliver get caught in the first place. After that, all four (even the reluctant Nancy and Dodger) agree to get Oliver back just in case he peaches on them.