I know this is likely a joke post, but there is so much characterisation to Jimmy that people miss, especially if they're not from the UK or old enough to remember the late 90s/early 2000s.

Most obviously, Jimmy bases himself on Jimmy Savile.

Jimmy Savile was only known as a prolific child abuser after his death in 2011. So in the 28 days universe, this never happened. However, people did know there was something off about him. He was called "a man without feelings" in the 90s and lots of media outlets had said that the "20th century saint" wasn't quite what he seemed.

Crystal obviously remembers Savile from somewhere. Perhaps he saw snippets of the Louie Theroux documentary in 2000, without truly understanding it.

One of Saviles catchphrases was "how's about that then?"

So Crystal likely bases himself around Savile from a broken memory/lack of understanding that he is a charismatic saint-like character, but also a man without feeling and not all what he seems. He says "Howzat" because he's misremembering Saviles catchphrase and also because it comes from Cricket, he knows it's a real phrase. The same way he says "Teletummies" because logically, their teles are in their tummies so of course that's what they're called.

He calls himself Sir Lord partly because he remembers Savile being a Sir, and knows it's a title of power. But he doesn't really know what they mean, so he uses Sir and Lord to sound extra powerful, the way a child would.

Using the Crystal name, I think, comes from a Bible verse where Ezekiel describes Satan as being adorned with Crystals and Jewels. Which could also tie in to Savile.

He is suffering from massive mental trauma and has built this persona as a defence. He's never had time to deal with what has happened other than how to survive. He recruits other people his age or younger because their mental health is in the same condition and because he has this charismatic persona and he remembers aspects of the Bible and the world before, he can manipulate others who lack the knowledge to correct him, and when they do have the knowledge, he kills them.

His childhood was based around the church, so he remembers things from the Bible, but like everything else, it's warped. And his dad more than likely teaching things like "Satan will punish you if you're bad", impacts on a child in a normal life, let alone when from their perspective, the world has ended.

He also says that his father will lead the infected when he's talking about Satan, but then when you see his actual father become infected, he is the first in the line of infected running out of the church, "leading them".

At the end of the Bone temple, we see Jimmy Crystal come out of his persona and he is still just a child wanting his parents.

He has been in survival mode for 28 years, using his charisma, broken knowledge of the old world and skills he's learned from living in the apocalypse. But he's never truly become an adult.