The Black Butterfly Gang is an International Spy Ring who specialize in stealing military and scientific secrets to sell to the highest bidder.
There have been different leaders of the The Black Butterfly Gang, the first being, Evil Jaw who is killed in the episode: Evil Jaw and the Devil Germs. Also seen leading the Black Butterfly in a couple of episodes is the infamous Dr. Ghost a brilliant scienist who like Dr. Spectra has turned to crime, finding it to be more lucrative, no doubt.

Dr. Ghost makes his debut in the episode, "Seven Days to Terror" and is also featured in "Target, 8th Man" with Agent Byrd.
In the episodes "The Threat of Disaster", and "The Atomic Ghost" the Black Butterfly Gang seem to be leaderless, except for a man named, Mr. Karsh, the overseer of Mr. Barret - the "Ghost".

Black Butterfly Gang members are all indentifed by a small tatoo of a black butterfly (what else?) on their wrists. The Black Butterfly Gang attempts to destroy 8th Man in the first episode they appear in; then in subsequent episodes they want to capture him, so they can sell him for big bucks.