Some new information about Jonah's life came to light in MAG 161, and it inspired me to compile a timeline of what we know about him. Here is it in all its incomplete glory!

Unknown Date of Birth

1815, Spring. Visits Albrecht von Closen to talk about his interest in the esoteric. (MAG EDIT: 23)

1. Robert Smirke begins work on the Millbank Prison, presumably with help from Jonah.

2. Jonah founds the Magnus Institute. (MAG 1 and 23)

3. Millbank prison is completed. (MAG 41).

1824, April. Barnabus Bennett asks Jonah for help escaping what is presumably the Lonely. Jonah does not intervene and watches Bennett suffer. (MAG 92)

Note: at some point, Jonah picks up Bennett’s bones, and they are still in his office in the Institute.

1. Jonah sends Doctor Jonathan Fanshawe to see Albrecht Von Closen, who has developed a strange and serious illness. Receives a letter from Dr. Fanshawe blaming him for Von Closen’s death and asking that they never speak again. (MAG 127).

1867, February. Receives a letter from Robert Smirke begging him not to wear the Watcher’s Crown. (MAG 138).

Note: Robert Smirke dies the same day that he wrote the letter to Jonah. It is unclear if Jonah used his powers to kill Smirke (MAG 138).

1. Millbank prison is demolished. (MAG 41).

Note: Jonah’s original body is in the panopticon in the remains of Millbank prison, underneath the Institute (MAG 158). EDIT: We don't know for sure when he put his body there.

1965 (Roughly). Gertrude starts work at the Magnus Institute and meets Jonah in the body of James Wright (MAG 158).

Note: Since Gertrude says she knew Jonah as one other host besides Elias in MAG 161, it’s safe to assume Jonah had already taken over Wright before Gertrude joined the Institute. This means he became a full avatar and gained body-hopping abilities somewhere between 1867 and 1965, assuming he wasn’t already a full avatar when he received Smirke’s letter. If he killed Smirke via Eye powers, he was an avatar already, but I can’t find convincing evidence one way or the other in MAG 138.

1. OG!Elias is employed at the Institute. This is contradicted by MAG 49 later, so it’s unclear if it is accurate information. (MAG 29).

2. Jonah!James Wright takes over as head of the Magnus Institute. (MAG 49)

Note: It's possible Jonah did not possess James Wright until this year since this is the year Wright starts heading the Institute.

1. OG!Elias joins the Magnus Institute (MAG 49). Again, unclear which date is correct.

2. Jonah Magnus moves host bodies. He leaves the body of James Wright and enters the body of Elias Buchard by gouging out his eyes and replacing them with his own. Jonah!Elias (J!Elias from here on) then takes over the Institute. James Wright “dies” (read: Jonah abandons his body) (MAG 49).

2015, March 20th. J!Elias foils Gertrude’s plan to destroy the archives and kills her. (MAG 158).

2018, September. Reveals himself to Martin as Jonah Magnus. Foils Peter Lukas’ plan to kill his original body, which would have destroyed him. (MAG 158).

2018, October. Launches the final phase of his plan to complete his version of the Watcher’s Crown, using the Archivist as a conduit. Gloats excessively. (MAG 160).

Note: I am assuming that James Wright and Elias Bouchard died when they were possessed. This was never explicitly confirmed, but people usually don’t survive horror-possession in this canon.

Note: Chuckling a bit at the fact that Jonah has to pick host bodies with similar eye colors.

And that’s everything I could find with a few hours of digging. HUGE shoutout to the Wiki and official transcripts for making my life so much easier! I want to reformat this so it’s easier to read, but I want to make sure I didn’t miss anything. If you feel like it, give it a read through and let me know if I missed/misinterpreted anything.