As for the Jigsaw Killer himself, aka John Kramer?

Source: https://www.slashfilm.com/1408494/saw-box-office-smash-biggest-horror-franchise/

Besides the allure of its central killer, John Kramer, aka Jigsaw (Tobin Bell), audiences flocked to the theaters to see the kill sequences.

Source: https://www.slashfilm.com/1253461/best-horror-movie-franchises-ranked/

Diagnosed with terminal cancer, the desperate serial killer John Kramer travels to a shady clinic in Mexico in the hopes of lengthening his time on earth by any means necessary.

Source: https://screenrant.com/saw-10-shawnee-smith-role-adam-return-hint/

Instead of ending John's transformation in Jigsaw, galvanize his convictions and represent the moment John Kramer truly starts to embody his judgmental homicidal alter-ego.

Source: https://screenrant.com/saw-movies-jigsaw-john-kramer-origin-explained/

Regrettably, as time passed, the long-running series started to feel repetitive, almost like a never-ending soap opera introducing new disciples of John Kramer just to keep the story chugging along.

Source: https://www.cinemablend.com/movies/saw-x-has-higher-reviews-than-any-other-movie-in-franchise

So far, the only two cast members to be revealed are Tobin Bell, who will be playing John Kramer, and Shawnee Smith's Amanda.

Source: https://screenrant.com/horror-movies-2023-release-dates/

They follow a former machinist named John Kramer (Tobin Bell), a.k.a. Jigsaw, as he kidnaps his victims and locks them into outsized metal death traps outfitted with some sort of time-release widget.

Source: https://www.slashfilm.com/1406084/saw-composer-manipulates-music-to-drag-audiences-into-dismal-pit/

Though John Kramer, aka Jigsaw Killer, died at the end of the third movie, it is revealed that he had already planned ahead of his death and left behind clues and recordings for the next game.

Source: https://www.comingsoon.net/guides/news/1327878-saw-iv-where-to-watch-stream-online