John Gregory is the engineer on the HMS Erebus in the Discovery Service for the British Royal Navy.
During the events of The Terror: Season 1 Episode 1 Go for Broke played by Mike Kelly
A large piece of ice hits the Erebus and Billy Orren falls overboard. Gregory alerts the rest of the crew and Charles Des Voeux and Henry Collins throw ropes towards Orren, but Orren sinks into the water. John Franklin calls a meeting of the officers, including Lt. H.T.D. Le Vesconte, and Gregory tells them about the damage to the Erebus and Francis Crozier warns Franklin that they will be dealing with pack ice ahead. He asks Lt. Graham Gore how many sun dogs he has seen and suggests they explore King William Land to see if it is an island and Thomas Blanky agrees. Franklin decides against his advice and James Fitzjames considers Crozier's warning, melodrama. Crozier then angrily points out that only four people at the table are veterans of the arctic, but Franklin again decides to continue on. Franklin gives a speech to the crew about how they will soon accomplish their journey. Six days later, both ships are stuck in the ice and the next morning they wake up to be surrounded by continuous ice.
During the events of The Terror: Season 1 Episode 2 Gore played by Mike Kelly
Spring, 1847, Gregory shows Franklin and Fitzjames the engines on the Erebus and they talk about which survey crew will be successful.
During the events of The Terror: Season 1 Episode 5 First Shot a Winner, Lads played by Mike Kelly
Lt. Edward Little walks to where Lady Silence is being kept and finds trinkets sitting outside her room and Gregory tells him, the trinkets are removed every morning, but more show up. Henry Goodsir, who was sitting next to lady Silence, hears Little tell Gregory that Lady Silence is being moved to the Terror. He asks if he can come as he is working on a Inuktitut dictionary with Lady Silence.