system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is "The Monster" in Group Theory?

I've seen a few videos online describing how mysterious "The Monster" is, and how it was even described as "The voice as god" by its discoverers. 

I don't have any experience with Group Theory or e8 lattices or whatever, this topic sounds cool and I just want to understand it further.
gpt
Group theory in some sense studies types of symmetry. For example, an equilateral triangle has a three fold symmetry whereas a square has a four fold symmetry. These symmetries are objectively different.

Mathematicians were interested in knowing all the types of symmetries. So they categorized tons of them. Thing of symmetries as chemical compounds. It turns out that some symmetries are really composites of two simpler symmetries. Like 6 fold symmetry may really be a composite of 2 fold symmetry and 3 fold symmetry.

It turns out that all all finite symmetries are really just compounds of a set list of simple symmetries. Simple symmetries are symmetries that cannot be broken down. So simple symmetries are like chemical elements of symmetry. The monster is a huge simple symmetry. Normally simple symmetries are much smaller. It is very unusual that such a large symmetry has no constituent components. 

It would be like there was a random element of astronomical size compared to the other elements like Oxygen and Carbon.