Nothing is known of the criminal known as Dmane prior to his arrest in the year 6946 A,D,  5000 years in the future, humanity had learned to attune themselves to the magnetic forces in the Earth, giving them powers to enrich their lives and ease their burdens.  As a result, 500 year since developing this ability, war had become largely obsolete.  Dmane, on the other hand, elected to choose a more barbaric role, attempting to use his powers to subdue his ordinarily pacifistic world.  Ultimately defeated, Dmane was sentenced to death for his unrepentant crimes.

Meanwhile, 5000 years in the past, Jay Garrick was experimenting with new technology to "Go fishing" in the timestream and pull back solid objects for him to study and develop in the 20th century.  On it's first test,  the device snatches Dmane from the executioner's platform, sparing his life and unleashing him in Keystone City.  Quickly realizing his good fortune, Dmane vows to conquer the past.  Garrick attempts to reverse his device and return Dmane to the future but the villain using his magnetic powers to destroy it.  Switching quickly to his identity as the Flash, Garrick engaged Dmane but the criminal's magnetic powers paralyze him.  Applying combustible chemicals to the Flash and Joan Garrick, Dmane leaves them in the path of a telescope that will focus the sun's rays as it passes and ignite them.

Dmane makes his way to a radio statio where he announced his intentions to the rule the Earth and to demonstrate his might, reveals that he will rob the National Mint.  Police rally to head him off but Dmane arrives in brazen style, stalking up the front steps and turn the police's guns against them.  When they flee inside to barricade the door, Dmane pulls the steel out of the walls around them.   Meanwhile, the Flash has managed to vibrate free and insuring Joan's safety, races to police headquarters to catch up Dmane's whereabouts.

As the futuristic criminal reached the vaults, the Flash arrived and moved too quickly in the open space for Dmane to draw a bead on him.  Zipping around behind him, Garrick tested a theory that the magnetic powers of the future were based on contact with the Earth and when he lifted Dmane's feet off the ground, the criminal's ability to channel magnetism dissipated.   Seizing the advantage, the Flash circled the globe at faster than light speed and clued in to Dmane's origins by the dials on his machine, was able to deposit him back on the executioners platform at the precise moment he had disappeared (Flash Comics Wheaties Giveaway 1946).

Whether Dmane was actually executed or had future criminal activities is unknown.