King Cobrawas a teen-aged delinquent and one of Dr. Able Cuvier's original three test subjects who was spliced with the DNA of a snake (specifically a cobra if his name is any indication) which gave him great agility. Along with Ramrod he was the first of Cuvier's "children" encountered by Terry McGinnis aboard a subway train. Later King Cobra was sent by Cuvier to murder District Attorney Young, but was stopped by Batman. Later, he was the first of the teens to be turned back to normal by Batman using the mutagen antidote.
Although King Cobra had fangs in his snake form, and did in fact bite Batman at one point, it is not known if he was poisonous.