Ygor is the main antagonist in the films, The Son of Frankenstein and The Ghost of Frankenstein. He "befriends" the Monster and uses him for his own purposes of revenge. He is portrayed by Bela Lugosi, the actor best known for playing Dracula.
Not much is known about Ygor's life prior to the films he is featured in. It is known that he was a blacksmith in the village of Frankenstein. He was arrested and convicted by a jury for stealing bodies. It is not by any means certain who he stole the bodies for, but he does mention that he "knew" Henry Frankenstein in Ghost, so it is not outside the realm of possibility that they were collaborators at one point. The villagers hanged Ygor and the town doctor proclaimed him dead. Not wanting to bury him on consecrated ground, the villagers dumped his body in the ruins of Frankenstein's laboratory. However, Ygor wasn't dead, but his neck was twisted and deformed. He went mad and thirsted for revenge. Some time after this, Ygor stumbled upon the Monster and gained his trust. Ygor took advantage of this and convinced the monster to kill the men who condemned him. However, the Monster only managed to kill six of the eight members of the jury when he was struck by lightning and rendered comatose. This put Ygor's revenge on hold for a period of several years.
Wolf von Frankenstein
After an unspecified period of years, Dr. Frankenstein's son Wolf, also a scientist, returned to his family's ancestral home, having been brought up in England. He was determined to clear his father's name and rectify the mistake made many years before when Henry's assistant Fritz mistakenly stole a criminal brain, which Henry placed inside the Monster. Ygor met Wolf when he went to explore the ruins of his father's laboratory. Realizing that Wolf could revive the Monster given enough time, Ygor showed him where the Monster had been hidden, in the Frankenstein family crypt. Wolf restored his father's equipment and began experimenting on the Monster, hoping not only to bring him out of his coma but also to fix his brain as well. However, once the Monster regained consciousness, Ygor put him to work completing his plan of revenge. He even has the Monster kill Wolf's butler Benson in order to keep him from anyone about the Monster still living. After Wolf learns what Ygor has done, He goes out to the laboratory to confront him. Ygor attacks Wolf with his hammer, but Wolf riddles him with bullets. In a climactic fight scene, the Monster is hurled into the laboratory's sulfur pit by Wolf.