[Buffalo Tom]

During WWII, the Nazis had various research programs to develop new weapons for the war effort. One of these research groups delved into the supernatural. In the waning days of the war, this group attempted bring forth the ultimate weapon. On a remote island off the coast of Scotland, Nazi occultists and scientists worked to combine science and the supernatural to bring about this goal. Led by the monk Rasputin one night in 1944, they began a ceremony to bring about Ragnarok by opening the gates of Hell on Earth. Before the rites could be completed, a small band of Allied GIs, led by Professor Broom, interrupted the event. The gate was open long enough, though, to admit one thing from that Hell dimension: a baby demon. Professor Broom immediately took hold of the creature and named it Hellboy. Hellboy was raised by his surrogate father, Professor Broom, and went on to become a field agent for the Bureau of Paranormal Research & Defence.

It is revealed later in the series that Hellboy is half human, the child of a demon father and a human mother.