The Molecular Master was an android created by the Time Trapper to steal the Miracle Machine from the Legion of Super-Heroes. He tried to do this by applying for Legion membership and once accepted, poisoning the Legionnaires. This plan was stopped by Wildfire, who who figured out that Molecular Master was a machine and destroyed him.
Later the Molecular Master returned when the Time Trapper sent him to the past to destroy Superboy and the Legionnaires who were in the past with him. The Legionnaires combined their attacks to once again defeat the Molecular Master.
The Molecular Master has the ability to break molecular bonds and reconfigure the resultant released energy into blasts and force shields.