As Stoker wrote him, R. M. Renfield is 59 years old, of sanguine temperament  and great physical strength.  His morbidly excitable  nature is interrupted by periods of gloom.  There is no mention of where he has come from, how long he has been a patient at the sanitarium, or what his occupation was.

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.