Jared Malahyde was a human and an aspiring poet in 1831. He was contacted by the Eternine in order to "preserve" humanity. He was possessed by Watchlar, who used him to create the Utopian Engine, Malahyde acquiring the necessary resources by a business alliance with Isambard Kingdom Brunel thanks to Watchlar's advanced knowledge. However, instead of saving humanity when it was activated in 1843, the Utopian Engine made it age forty years in forty seconds- known in the future as 'The Cleansing'- killing most humans on the planet. Malahyde then spent five years in his home working out a way to fix what had happened to humanity, the time dilation effect of the Engine meaning that a hundred and sixty years passed outside the machine.
When the Eighth Doctor arrived in this timeline in 2003, he attempted to undo it by going back to the day of the Cleansing and contacting Brunel, who was able to direct him to the day when Malahyde first met him. The Doctor was able to rescue Malahyde's past self before the Eternines could tell him their story, but the new timeline was too solid now for the Doctor to erase it in that manner. When the future Malahyde was killed by Watchlar, the Doctor was able to use the Utopian Engine to turn time back to the day when he had rescued the past Malahyde. The younger Malahyde departed the TARDIS, but the Doctor solemnly noted to Anji Kapoor that he was unlikely to ever succeed as a poet as neither of them had ever heard of him. (PROSE: Reckless Engineering)