Manfred Mota is a nuclear engineer, and the father of Valerie Perez. He was introduced in the Flash 50th Anniversary Special as having faced multiple incarnations of the Flash, each time using a new moniker, but similar powers.
On his first appearance as the Atom Smasher, he uses his knowledge as a nuclear engineer, to create a suit giving him an atomic-power punch. Mota is defeated by Jay Garrick.
In prison, Mota plots revenge and when the new Flash, Barry Allen, appears, Mota believes him to be Jay. Released from prison, Mota holds Central City hostage as Professor Fallout, secretly hiding a neutron bomb in a sculpture of an atom. He is quickly defeated by Barry and returned to prison.
During his second stint in prison, Mota begins to obsess over revenge, the Flash and safe nuclear power. Creating the identity of Fusionn, Mota steals equipment from a nuclear power plant and crafts a suit that allows him to shoot blasts of energy. Mota manages to unmask the third Flash, Wally West, in the fight, only to realize that he is not fighting Jay, and that West's identity is publicly known. Enraged, Mota attemps to melt the entire city, but West throws a stone through one of Mota's cooling tanks, melting the suit into radioactive rock.
One Year Later after Infinite Crisis, Mota's daughter, Valerie, has begun a romance with the fourth Flash, Bart Allen. Mota somehow has been transformed into an energy being, and has been stalking his daughter. He kidnaps her with the help of Allen's clone Thaddeus Thawne (Inertia). Mota plans to use his daughter's DNA to reconstruct his own body, but is doublecrossed by his partner. Manfred later appears to Valerie again, claiming that he still loves her, but is captured by Bart Allen.
The future Flash, John Fox, faces Mota when he returns as a monster made of living Plutonium in 2645. Fox manages to send Mota into the future where he decays into lead.