Little is known about the origins of Mortimer Toynbee. As a deformed baby of English descent, he was abandoned by his parents so early in his childhood that he could not remember them.  At some point, he became an experiment for the Black Womb Project run by Amanda Mueller in Alamogordo. After categorizing Toynbee as a mutant reject due to his flawed genetic template, Mueller wished to see how his natural development would progress. Eventually, Toynbee was placed in an orphanage where the other children continually tormented him, regarding him as a freak due to his ugliness, his unusual physique, and his leaping ability. Toynbee was so traumatized by his loneliness and the continual abuse he received that it affected his learning abilities. The teachers and administrators in the orphanage therefore regarded Toynbee as mentally challenged, even though, in actuality, he had a rather gifted intelligence. So desperate did Toynbee become for affection that he developed a pathetically subservient personality and unquestioningly obeyed anyone he thought sincerely cared about him.

As a young adult, Toynbee was a victim of a lynching in Manchester, when he was discovered and saved by the master of magnetism Magneto. Judging Toynbee to be strong, Magneto recruited him as one of the first members of the Brotherhood of Evil Mutants, with aims of carrying out a mutant supremacy agenda. Magneto gave Toynbee the alias of the Toad after his abilities, appearance, and personality. Although being given shelter and purpose, Toad was treated by Magneto as a jester who was expected to follow orders unquestioningly. Pathetically devoted to Magneto, the Toad blinded himself to Magneto's continual verbal and physical abuse

When Professor Xavier and Magneto founded a mutant exclusive island nation on Krakoa, the Toad became one of its citizens. Alongside Mystique and Sabretooth, he was sent by Xavier on a mission to steal information about the Orchis Forge from Damage Control. Due to the Toad's exceptional hacking abilities, they were successful and escaped, only leaving Sabretooth behind due to the intervention of the Fantastic Four.

Toad's primary power is the ability to leap to heights and distances far greater than that of an ordinary human. He possesses a degree of superhuman strength, particularly in his back and legs, which grants him his superior leaping abilities.