Question: Is the Sufferer actually Troll Jegus?
Hussie: Terezi mentioned Troll Jegus in a joking exchange with John a while ago. Whether the Sufferer's name is actually Jegus, and whether or not she actually knew anything about this story when she said that, is left to your speculation.
This ancestor interlude is a little religious tale. Over the course of the story sometimes we wander into these silly mini-genres, like "horrorstuck", or erotic historical fiction through Mindfang's journal entries.
The Jesus parallel is pretty blatant, down to the use of the torture device as the symbol for the religious movement (cross, irons). I personally think the explanation of the relevance of Karkat's sign is one of the more interesting aspects about it, just from the perspective of taking existing symbols and adapting them to an evolving mythological framework. Segments like this aren't really just about "Gee, the ancestors sure are cool, let's hear more about them." (Though there's no question there's a certain amount of fan service in play when I do stuff like this.) We learn more about the story and characters and answer questions beyond the limited scope of their biographies, like why Karkat had a sign at all if he had no caste.
We learn more about the troll race, as a once peaceful species and such before kid-ancestors as players scratched their session, though the short term relevance of this is mainly as a preamble to Scratch's religious story. Establishing an Eden-like paradise from which there is some departure through sin is sort of the boilerplate basis for religious lore.
Scratch is a devil figure about as blatant as the Sufferer is a Christ figure. The failed players from peaceful Alternia made a classic "deal with the devil" move by causing the scratch after being given a choice by the mother of all monsters. (Echidna. Hey, she's a big snake!) By doing so they brought Scratch into their universe, and therefore all the things you'd expect that comes with summoning the devil. This resulted not only turning Alternia into a planet full of violent murderers, but it only technically granted them what they wanted with a huge caveat, as is the case with such ill-advised bargains. The players were strong enough to win, but made a terminal universe, were barred from entry, hunted by a demon, and then started killing each other.
"Old Scratch" is actually an old timey nickname for the devil. It's used in some Twain books. The manipulative devil figure pulling the strings was always the basis for his character, and this was probably pretty obvious right away. He's part devil/puppet/cueball, with a dash of the old gambler/gunslinger Doc Holliday in his profile. Doc Holliday is actually my ancestor. He is related to me on my mother's side, who's last name is also Holliday.
Hopefully I won't die at age 36 of tuberculosis though. If there's anything to the karmic fortune-swapping of the trolls and their ancestors, ideally tuberculosis will die of me.