Jon is a teenaged sorcerer from the comic, The Last of the Viking Heroes.
History
In The Last of the Viking Heroes Summer Special issue 2, he acquired a potion from his mentor, Zon, that would allow him to handle any situation when consumed. Later, at Jon's birthday party, he is given a sack of Ninja weapons pillaged "from the Orient" and some turtle soup. Thinking the soup would make the potion taste better, he mixes some into the potion.
Some mercenaries that Jon had angered earlier come to attack him, and he drinks the potion. With the combination of the turtle soup in the potion, and the Ninja weapons in proximity, he becomes, as his friends declare, a "Teenage Mutant Ninja Turtle." After dispatching his foes, Zon arrives and restores Jon to his human form with a blast of magic, and chastises his protégé for tampering with the potion's formula. Says Zon: “The combination of mutagen and turtles are reserved for future wizards. I believe their names will be Kevin Eastman and Peter Laird”.
In The Last of the Viking Heroes Summer Special issue 3, Professor Zion goes back in time to 1048 A.D. in order to steal Erik's legendary sword so he can rule. Erik and Tomgar unsuccessfully battle Brazer, one of Zion's robots. Tomgar is blasted and thinking him dead, Erik prepares to attack once more, but Jon stops him. Jon urges a retreat in order to form a strategy. The Turtles, who have been spying on Zion, use his time machine to travel to the palace. They arrive and Erik, thinking they are demons, starts to charge at them. Jon grabs his arm and say that in some strange way, he knows these creatures (see issue 2) and believes they are there to help.