Once a fugitive from America on the run for multiple counts of capital murder, Jack found himself warped into Gensokyo. He managed to join the ranks of the local Human Village Militia, and would take over as its de facto leader. His leadership gradually corrupted the militia's noble goals of defending humans into anti-Outsider violence... or whatever new political excuse he makes up to justify his continued murder spree without the cops around. He effectively believes himself as the savior of the Japanese people living in the village... (As if that doesn't sound awfully like something an otaku with no self-awareness would say.)

Come December 2015, he immediately set sights on an amnesiac Kazuki Murasaki, wandering around the village to find his way around Gensokyo, and wasted no time attempting to ambush and murder him. After his first attempt was foiled by Sanae Kochiya, he would make numerous other attempts to attack Murasaki and his growing family.

By the time Murasaki had reunited with his sworn brother, Taiga Hamjima, Jack made one last desperate attempt to reclaim his unquestioned power over the village... by waging war on the Murasaki Family... right at the Moriya Shrine's front doors all the way on Youkai Mountain... with Sanae, Kanako and Suwako on Murasaki's side. (Yeah, sure, that totally isn't suicide...)

Of course, Jack and his goons failed... and he certainly didn't get lucky with a last cowardly attack on Murasaki from behind, if Hamjima didn't tackle and incapacitate the fucker.

Based on the character of Jack the Collector from Pirates in Hawaii, but openly more sadistic, self-absorbed and maniacally blood-thirsty... It is unclear exactly how he's related to Jack the Collector though.