R. M. Renfield is a fictional character who appears in Bram Stoker's 1897 Gothic horror novel Dracula. He is Count Dracula's deranged, fanatically devoted servant and familiar, helping him in his plan to turn Mina Harker into a vampire in return for a continuous supply of insects to consume and the promise of immortality. Throughout the novel, he resides in an asylum, where he is treated by Dr. John Seward.

In the various film adaptations of the novel, he has been portrayed by actors such as Alexander Granach, Dwight Frye, Roland Topor, Tom Waits, Peter MacNicol, Simon McBurney and Nicholas Hoult.

A description of Renfield from the novel:

R. M. Renfield, aetat 59. Sanguine temperament, great physical strength, morbidly excitable, periods of gloom, ending in some fixed idea which I cannot make out. I presume that the sanguine temperament itself and the disturbing influence end in a mentally-accomplished finish, a possibly dangerous man, probably dangerous if unselfish. In selfish men, caution is as secure an armour for their foes as for themselves. What I think of on this point is, when self is the fixed point the centripetal force is balanced with the centrifugal. When duty, a cause, etc., is the fixed point, the latter force is paramount, and only accident or a series of accidents can balance it. — From Dr John Seward's journal

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. Seward diagnoses him as a "zoophagous maniac", or carnivorous madman. Later Renfield attacks 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 behaviour 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 much like Dracula himself.

However, when confronted by Mina Harker, Dracula's latest victim, 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 he was convinced 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 against 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."