Grodd

The second Flash, Barry Allen, first came into conflict with Grodd in the early days of his career as a Super-Hero. While he had already encountered criminals like Captain Cold and the Weather Wizard, Grodd was on another level compared to the villains he had encountered before. Solovar, an ape from the hidden Gorilla City, was pretending to be a regular gorilla in the Central City Zoo, when he contacted the Flash to warn him of Grodd's plans to conquer the human world.

He explained to the Flash how he and his people came to be, telling him that he was once a regular ape until an alien spacecraft crashed in his African jungle home. The local tribe of apes were then changed when the ship's alien pilot granted them incredible intelligence and mental powers, giving them all telepathy and telekinesis. The alien then helped them all build Gorilla City, where the apes chose to live in peace, apart from humanity, with technology more advanced than any human's. But the gorilla named Grodd was corrupt, and believed that the apes should take over humanity, and appointment him as their ruler.

There the residents of Gorilla City lived in peace for many years until their home was discovered by a group of explorers. Grodd then forced one of the explorers to kill the alien who granted them their powers, and he took over Gorilla City, from where he planned to take over the entire world. The ape Solovar journeyed to the outside world for help, and contacted Barry Allen to warn him of the evil gorilla's plans. Once Grodd was defeated by the Flash, he was able to temporarily remove Grodd's mental powers.

Grodd's powers eventually returned, and for the next several years he makes many attempts at destroying the Flash, with schemes involving transferring his mind into that of a human being (alternately named Drew Dowdon or William Dawson), taking away the intelligence of his fellow apes from Gorilla City, and even faking his own death, and transferring his mind into that of a regular ape from the Central City Zoo. When fighting the Flash solo didn't pan out for him, he would team up with several other world conquering villains on many different teams, but he always wound up defeated and imprisoned by the Scarlet Speedster.