Isaac is a supporting character in the Doctor Who episode "A Town Called Mercy". He served as the Marshal of the small western American town Mercy in 1870. He is portrayed by Ben Browder.
History[]
Prior to the episode's events, Isaac welcomed alien scientist Kahler-Jex into Mercy and offered him protection from the cyborg assassin known as the Gunslinger. Jex was a welcome addition to the town, using his scientific expertise to provide Mercy with a rudimentary electrical grid that ran off his ship's generator and also providing treatment for an outbreak of cholera.
In 1870, the Gunslinger arrived on Earth and effectively cut off Mercy from the outside world, preventing the town from receiving any trade or reinforcements. The Gunslinger demanded Jex, but Isaac and the other townsfolk refused to hand him over.
Three weeks after the Gunslinger embargoed the town, the Eleventh Doctor arrived along with Amy Pond and Rory Williams. After meeting Isaac and Jex and learning of the town's troubles, the Doctor offered his aid and went back out into the desert where he had left the TARDIS. However, he didn't go back to the TARDIS and instead found Jex's ship, accessing its main computer and finding out why the Gunslinger was after him.
Realising that Jex was a war criminal who had killed countless people during the Gunslinger's creation process, the Doctor was prepared to force Jex out of town and let the Gunslinger have him. Isaac objected to this, not concerned about Jex's past but rather all the good he had done since coming to Mercy. The Gunslinger came for Jex and raised its arm cannon, but Isaac shoved Jex aside just as the cyborg fired and was struck by the blast. As he lay dying, Isaac told the Doctor to protect Jex and the town, appointing him the new Marshal.