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Jacob Russell is a werewolf appearing in Marvel Comics.

Jacob Russoff (Later changed to Russell) was the elder of two children sired Gregory Russoff, a Transylvanian baron and scholar. Russoff's ancestor Grigori first brought lycanthropy upon the family when in 1795 he tried to rescue his wife, Louisa, from the vampire Vlad Dracula and was bitten by a werewolf. Consequentially Grigori's descendants carried the curse of the werewolf. They only needed a catalyst to trigger it. In the mid-1950s Gregory Russoff, great-great-grandson of Grigori, acquired a copy of the Darkold, which includes the secret origin of lycanthropy. By reading that passage, Gregory activated the curse and became a werewolf. He sent his wife, Laura, to her native America with their children for their own protection. Gregory was eventually killed by an angry mob. Laura Russoff married again, to a man named Russell. Jacob Russoff became Jack Russell, and with his sister Lissa was raised in Los Angeles. When he turned 18, the curse struck him in turn and he became a werewolf. For about two years, Russell became a werewolf by night during the full moon. He took precautions to lock himself up, but sometimes the wolf escaped. During that time he never took a human life, although several of the persons he encountered were scarred or crippled.
Mysterious beings known as "The Three Who Are All" magically altered Russell's curse so that he could change shape voluntarily and retain his human intellect while transformed. Unfortunately, the curse still applied on nights of the full moon, when the wolf's mind supplanted Russell's. He designed a virtually escape-proof cell for those times. Russell worked with Dr. Karl Malus, a medical researcher in L.A., to find a cure for his problem. But he found that Malus's treatments had unintended consequences. He lost control over his transformations, and his werewolf form became even more lupine, with longer ears and snout, curved spine, and canine legs. A devil-worshiping cult led by Schuyler Belial tried to capture Russell for use in a satanic ritual. If they sacrificed a werewolf and transfused his blood with theirs, they believed they would become werewolves themselves. For almost a year he fled from the cult. With help from Moon Knight, Russell finally confronted the cultists, and murdered several in battle. He approached by the vampire scientist, Dr. Michael Morbius's who asked Russell to join his supernatural crime-fighting team, The Midnight Sons. He reluctantly agreed, though, mostly for the possibility of encountering someone who can lift his curse.