Jack Robertson

Jack Robertson was an American businessman. What he claimed to be a small part of his business empire, involved creating hotels around the world to make a large profit, creating the Robertson Luxury Hotels brand.

Robertson built his hotels on repurposed land, with the one in Sheffield having been constructed on top of an abandoned coal mine which was being used as a landfill site. He was not just aware of this, but he also knew that the waste in the landfill was toxic, but he willingly ignored it and turned a blind eye on it.

By 2018, he decided to run for the American presidency in the upcoming 2020 election. Apparently, he desired to do so because he hated then president Donald Trump.

In all of his hotels, he had underground safe rooms that he could lock himself inside if need be and live in isolation for roughly six months, catered by food, water, technology and weapons should he have to defend himself. He was vehemently against Great Britain's political ban on the use of guns in public use, thinking America was smart for allowing its citizens to arm themselves, considering shooting the problem to be "civilised."

When his bodyguard Kevin was killed by a mother spider, he joined the Thirteenth Doctor, Graham O'Brien, Ryan Sinclair, Yasmin Khan and Jade McIntyre as they tried to locate the source of what made the spiders so large. They eventually discovered the waste and planned to contain the spiders in a safe room. However, when they came across the mother spider, Robertson shot it dead and left. (TV: Arachnids in the UK)

Personality
Those around him tended to dislike Jack given he blamed them for things that were beyond there control, notably Najia Khan as he fired her for walking in on his meeting with Frankie Ellish, and "fired" her again for failing to cleaner a room full of webbing. He even thought she was behind the entire spider attack, simply because it was part of the Doctor's guesses.

Jack was a controlling and narcissistic man who spoke at length about his own business success, expressing incredulity and derision when the Doctor didn't know who he was. He generally treated other people contemptuously, firing Najia Khan on a whim even though she was only doing her job and hadn't really done anything to inconvenience him deliberately.

He never seemed to take responsibility for his own actions, and defended certain actions he saw as necessary. He viewed gunning down a defenceless and frightened spider as a mercy killing purely on the fact that it was already dying. Robertson clearly didn't intend it as a mercy killing. Robertson advocated the use of guns, thinking it civilised, and stated that his methods and way of thinking would get him into the White House.

He also displayed signs of paranoia, given his need for a bodyguard and speculating people were part of a conspiracy against him. (TV: Arachnids in the UK)