Who are Hellboy's greatest villains?

Some prominent villains of Hellboy’s include Grigori Rasputin, Baba Yaga, and Hecate, among others. Grigori Rasputin is the man that originally summoned Hellboy into the mortal realm. He plan was to use Hellboy for nefarious purposes to aid the Nazis in their plans. He also played a role in also releasing the Ogdru Jahad which would have led to the end of the world. He represents how unhuman a man can become contrasting how Hellboy, a half-demon, becomes humanized.

Baba Yaga is a character based on a witch from Slavic mythology that eats children, lives in a house on chicken legs stilts, and is able to fly. She is not able to overcome Hellboy’s strength but is able to trick him and give him a hard time. At one point, she forces him to surrender one of his eyeballs. Hecate, the Greek goddess of witchcraft as figure similar to Hellboy who instead of identifying with humanity, embraces her infernal destiny and becomes monstrous. As a result, she plays a good foil to Hellboy.