Gizmo is a genius inventor and weapons maker who specializes in creating deadly gadgets and weapons out of seemingly innocuous objects.
Having created a corporation which supplied technology to various people, including criminals, Mikron O'Jeneus, hoping to increase his wealth, donned the guise of "Gizmo" to join the newly formed villain group, the Fearsome Five.
After a number of unsuccessful conflicts with the Teen Titans and Superman, Gizmo went straight for a while and took a job at S.T.A.R. Labs until his former Fearsome Five teammate Psimon, after having been seemingly killed by his teammates, resurfaced looking for revenge, and shrank Gizmo to microscopic size. Years later, Gizmo found a way to revert to his normal size, and took up a life of crime once again, partnering with his former teammate, Mammoth.
Doctor Sivana later gathered the Fearsome Five to work for him in a scheme to short sell LexCorp stock by having them steal its accounts from its corporate building in Metropolis and then driving down the stock by killing all the people in the building, and destroying two other Lexcorp properties.
At the latter of the two the Five were confronted by the Outsiders and after escaping, the Five urged Sivana to take Lexcorp's nuclear missile facility near California. When Sivana refused due to the scheme having already ended successfully, Psimon asserted that they would take the nuclear facility anyway, and in response Sivana severed relations with the them after nearly killing Gizmo, warning them that he would kill them if they ever crossed his path again.
- Gizmo appears along with the other members of the Fearsome Five to support Raven's Evil Soul Projection when it is attacked.
- Gizmo patrols the edge of the Villain Stronghold in the Gotham Wastelands.
- Gizmo first appeared in in New Teen Titans #3 (1981)