A description of Renfield from the novel:
Renfield is an inmate at the lunatic asylum overseen by Dr. John Seward. He suffers from delusions which compel him to eat living creatures in the hope of obtaining their life-force for himself. Later Renfield's own testimony reveals that Dracula would send him insects, which he begins consuming. He starts with flies, the death's-head moth, then develops a scheme of feeding the flies to spiders, and the spiders to birds, in order to accumulate more and more life. When denied a cat to accommodate the birds, he eats the birds himself. He also changes his ideas to accommodate Mina Harker by quickly eating all flies and stating that it was an old habit. Doctor John Seward diagnoses him as a "zoophagous maniac", or carnivorous madman. Later Renfield builds up his own courage to harm Dr. Seward, acquiring a knife and cutting his arm; as Seward's blood drips from his hand, Renfield licks it off the floor.
During the course of the novel, the role of Renfield as a patient allows the reader to understand his behavior from the perspective of a psychologist. Through Renfield's demented mind, the reader learns the nature of a vampirism that is eventually revealed to be under the influence of Count Dracula; Renfield attempts to escape from the hospital multiple times to meet him. The vampire, whose abilities include control over animals such as rats, bats and spiders, comes to Renfield with an offer: if Renfield worships him, he promises to make him immortal by providing an endless supply of insects and rats, as Renfield believes that blood is the source of life.
However, when confronted by Mina Harker, the object of Dracula's obsession, Renfield suffers an attack of conscience and begs her to flee from his master's grasp. Consumed by his desire to keep Mina safe, he begs Seward and the others to allow him to leave lest he feel guilty for her fate. When Seward denies his request, Renfield tells the vampire hunters that "[he] warned them!" When Dracula returns that night, Renfield is again seized by his conscience. He remembers hearing that madmen have unnatural strength, and so attempts to fight Dracula. Renfield's strength leaves him after looking into Dracula's eyes, and Dracula throws him to the floor, severely injuring him.
The vampire hunters enter the room shortly afterward, and through an emergency surgery Van Helsing manages to prolong Renfield's life. Renfield tells how Dracula convinced him to invite Dracula in, detailing how Dracula entered the home and went after Mina. They leave him lying on the floor to rescue her. During the party's confrontation with Dracula in Mina's room, they manage to repel him with their crucifixes and wafers of sacramental bread, forcing him to flee the room. However, Dracula flees into other rooms and destroys their records, then back into Renfield's room to break his neck. "When Dr. Van Helsing and Dr. Seward had come back from seeing poor Renfield, we went gravely into what was to be done. First, Dr. Seward told us that when he and Dr. Van Helsing had gone down to the room below they had found Renfield lying on the floor, all in a heap. His face was all bruised and crushed in, and the bones of the neck were broken."