Monks is a dark, sinister figure who lurks menacingly in the background during much of the novel, a disaster waiting to happen. He sometimes appears without warning or identification. He is able to exercise much control over Fagin through his power to exploit the wily old thief's avarice. In any event, Fagin seems to fear Monks more than he does Bill Sikes. Monks typifies a kind of festering evil that works under the surface, manipulating the more obvious criminal types such as Fagin and his cohorts to do the actual dirty work and take the risks.
In Monks, we see another demonstration of the unsettling effects of an evil environment. In spite of an evidently comfortable background, he is a product of ill-will. The effect of this environment — particularly the moody, suspicious-natured influence of his mother — warps him in childhood to the point where his character is twisted for the remainder of his life. Monks forcefully illustrates that more than poverty is required to injure the human spirit; the absence of benevolence and affection are bound to have a controlling effect.