There is not necessarily any contradiction between a character being vivid and having a "dark" quality. Roald Dahl specializes in creating eccentric personalities who are both sinister and memorable, and in both "The Ratcatcher" and "The Hitchhiker," the titular character is unsettling and far from being conventionally charismatic. Both men are small, stealthy, and quiet, and both are described as looking like rats. Both also have forceful personalities that soon capture the attention of the reader and the other characters.

The ratcatcher introduces himself as a "rodent operative," while the hitchhiker describes himself as a "fingersmith" (a highly-skilled pickpocket). These grandiose titles for lowly (and, in the latter case, criminal) professions emphasize how seriously the men regard their work. Part of their curious attraction for their listeners is the depth and detail in which they describe what they do, as though it were the most important job in the world. Although the hitchhiker is a criminal, he comes across as a more benign figure than the ratcatcher, partly because he describes the moral code by which he operates:

I never takes nothin' from a loser. Nor from poor people neither. I only go after them as can afford it, the winners and the rich.

The ratcatcher, by contrast, seems more underhanded, as well as unnecessarily cruel and violent in his treatment of the rodents he resembles. He loses his listeners in the end:

Suddenly he noticed that his audience was no longer with him, that our faces were hostile and sick-looking and crimson with anger and disgust.

The other people at the filling station may not share the ratcatcher's absorption in his subject, but they will not forget him, and neither will the reader. Through his own unswerving conviction, he succeeds in drawing his audience into a world that they may well wish they had never encountered.