THE SHADOW.
For those of you who don't know, the 28th century leader of the Suliban Cabal, dubbed 'Future Guy' in fanon, and 'Shadow Boy' by me, had Enterprise been renewed and had they pursued the Temporal Cold War arc (seasons 1 and the first half of 2) instead of the Xindi War arc (the second half of season 2, season 3, and season 4), was going to be revealed to be none other than Archer himself. This has been confirmed by Brannon Braga.
What led Jon to become Shadow!Archer is that the Enterprise went down with all hands and he alone survived. He blames himself, and is all but debilitated by grief. He has lain in wait for centuries, undying, and causes the Temporal Cold War to rewrite that history.
Having sat around and watched the prime timeline (the timeline comprising of the Original Series, the Next Generation / Deep Space 9, Voyager, and culminating in the version of the 31st century Daniels is from), he is incredibly disappointed how things played out, and will stop at nothing to make a better future.
Given the Trek universe and the many reboots / soft reboots / things changing behind the scenes without an in-universe explanation, I reckon that Shadow!Archer has reset the timeline at least three times but it could be a lot more.
The first reset results in the timeline consisting of Discovery, Strange New Worlds, Lower Decks, Picard, and the 'bad future' 32nd century Archer and Daniels go to in "Shockwave."
The second reset results in the AOS timeline.
The third reset results in the 'final' timeline or the 'best' timeline, a timeline where the Xindi War doesn't happen, the Kelvin survives, the Burn doesn't happen, Captain Pike either lives (AOS) or is disabled but lives well (TOS / DIS / SNW), there's no Dominion War, and Voyager doesn't get stranded in the Delta Quadrant.
As a result, Shadow!Jon is ancient, jaded, and ruthless. He does not consider himself to be Captain Jonathan Archer, maintaining that Captain Archer died on the Enterprise with his crew. Though he loves deeply, fiercely, and all-consumingly, he could not care less about time, the universe, or himself. He is incredibly angry, eaten alive by guilt, and feels that what's happened is his fault to the point that he will remake time to his own design. He has nothing to lose, and he both doesn't care at all and cares so much to the point it destroys him. His best ending, he knows, is getting erased from history so that normal!Jon can live his life as he always should have, so if things don't work out this time, that's alright.
He's patient.
He can wait.
