Pro-Rata was descended from Egyptian sorcerers, Slavic witches, and Druids. He believed that all of these groups failed because the failed to see world domination in terms of accounting. He feels that the universe is the ultimate flow chart, and whoever can juggle the books can rule infinity.
Pro-Rata sought to obtain the Cosmic Key, aka the Jeweled Key to Pro-Rata's Cosmic Calculator to access its full power. To this end, he traveled to the extra-dimensional realm of Maltesia, where they Key was held by their chief accountant, Prei-Ying Mantis. Pro-Rata slew Prei-Ying by breaking his neck with a slide rule, and prepared to abscond with the Key. However, he was then confronted by Hemlock Shoals, a mystic and detective of Maltesia, who had been summoned by Prei-Ying, who suspected he might be attacked. Shoals knocked the Key from Pro-Rata's grasp as he opened an interdimensional portal, and the Key fell through a portal that accessed a myriad of realms. Pro-Rata fled and continued his search for the Key.
Pro-Rata had made a base out of a tower of credit cards on an island on Cuyahoga River in Cleveland, Ohio. For unknown reasons he kidnapped Beverly Switzler and imprisoned her in his tower. He planned to send his weredog (a man that can turn into a dog) to the Citadel of Sai-Fuur, where the Jeweled Key to his Cosmic Calculator had ended up. He planned this on the night when the stellar balance sheet came into alignment, so that he could reap the cosmic dividend when the astral audit was taken. However, that same night, Howard the Duck found and scaled the marathon, and killed the weredog after it attacked him when he attempted to rescue Beverly Switzler.
In order to obtain the key before midnight, Pro-Rata sent Howard and Beverly to the Citadel. They successfully obtained it, but when Pro-Rata summoned the back to his tower, he inadvertently hit the wrong decimal on his calculator, and also brought back the immense and powerful Bahnd-Bird which was attacking them outside the Citadel. Figuring the Key would make Pro-Rata too powerful, Howard refused to give it to him. Pro-Rata prepared to slay Howard, as well as Spider-Man, who had seen the shattering of the tower by the Bahnd-Bird. Howard ambushed Pro-Rata, tackling him from behind off the top of the tower. Howard was rescued by Spider-Man, but Pro-Rata fell to his seeming death.
However, Pro-Rata had indeed survived and set about investing his remaining mystical might to gain vengeance. After Howard and Beverly returned from a long trip, Pro-Rata ,having found a new mystical force bank in an abandoned tower in the Union Terminal, set about making his life more troublesome. He placed an advertisement in a newspaper about duck hunting season, and he used his flying cash register to crash Howard's taxi into another, causing him to get into a fight. Next he created a false movie studio in Union Terminal to lure Howard and Beverly into a trap, from which he could learn the location of the Jeweled Key. When he learned that Howard had hocked it, Pro-Rata sent his Eggsmen to attack them. Howard and Beverly defeated the Eggsmen and then unseated Pro-Rata from his cash register. Pro-Rata's power, unable to be repaid without the Jeweled Key, was then repossessed by the Astral Auditor. Pro-Rata fell into the collapsing vortex as the false realm of the movie studio collapsed in on itself. Howard and Beverly narrowly escaped the destruction of the vortex.