Who is Dennis from Creature of the Night and what is their importance?

Four-year-old Dennis is the second of two children born to an unwed mother. His mother, twenty-eight years old, and his older half-brother, Robert, comprise his family. Dennis' father abandoned the family, and although, he doesn't remember his father..... he does recall some details, mostly negative. For the majority of the novel, Dennis struggles to gain his mother's affection and attention. He is largely unsuccessful.