Sam Giddell was a scientist who furthered the research of Dr. Karos.
Sam Giddell worked with Dr. Karos on a special plastic which could become invisible by bending light (rather than absorbing it) when electricity was applied to it. However, the plastic became toxic to both the body and the mind after the current passed through, and this side effect prevented any further production. After Dr. Karos passed away, Giddell continued the work, hoping to eliminate the hazardous side effects, but with no success.
At some point, Giddell hired Lloyd Ventrix as an errand runner. However, Ventrix stole samples of the material and fashioned a suit for himself, using the invisibility to steal jewelry and money and to visit his daughter. Batman eventually met with Giddell, and used his information to track and apprehend Ventrix.