Origin

When Garko was first introduced, he was merely a peculiar man who was seen sitting on the fourth-floor ledge of an apartment in Cleveland, Ohio. It was stated that he'd sat there for days on end staring at a jar of juice he held, and occasionally shouting "I'm gonna conquer the world! You hear me?" As it turned out, Garko had been trying to decide on whether or not to drink the juice and use its power to conquer the world. At first he wasn't really sure if he really wanted to conquer the world, but he eventually decided it would be worth it since it would allow him to get rid of his enemies. Drinking the juice, Garko was transformed into the monstrous Garko the Man-Frog. 
It was never revealed just what Garko's juice was, how he'd acquired it, or just who his supposed enemies were.

Creation

Garko was created by Steve Gerber and Frank Brunner.

Major Story Arcs 

Frog Death!

After becoming the Man-Frog, Garko went on a brief rampage through Cleveland before coming afoul of an enraged Howard the Duck, who proceeded to whack him with a board with a nail in it. It was at that time that the effects of the juice that had transformed Garko went into overdrive, causing him to shrink and turn into a regular, harmless frog. Some police officers then arrived and arrested Howard the Duck, mistaking him for the rampaging humanoid animal that had been reported, and unwittingly ran over Garko the frog with their car.

Creator's Rights

Garko (in his human form) was last seen in a bar in Hell where Howard the Duck had a few drinks with God.

Powers and Abilities

As the Man-Frog, Garko was a creature of considerable size and strength, proving able to easily crush a car. He also possessed considerable leaping abilities due to his frog nature. These abilities of Garko were short-lived however, as he became a regular frog only a few minutes or so after transforming into the Man-Frog.