Jack Kowaczski was a teenager living in Jumpsville, Ohio.
In the fractured multiverse created by Sabbath's interference, Kowaczski invented the first time machine on Earth in the early 21st century. His trips backward created more and more alternate timelines, in many of which he died. One set included a Mars where life evolved from multiple versions of his decaying body dying in the planets' distant past.
The Eighth Doctor managed to fix the problems caused by the trips of the multiple Jacks. Two survived out of all the timelines. (PROSE: The Last Resort)