The Elder Scrolls is all about the retroactively "Chosen One," who's legendary, world-changing deeds are recorded in the Elder Scrolls (In case you can't tell from the title). And the story only begins once the character has the task that culminates in changing the world thrust upon him. In Arena, your character was chosen to overthrow Jagar Tharn by the ghost of Ria Silmane, first contacting you in the sewers of the Imperial Dungeon.
In Daggerfall, your character is chosen by fate to reactivate the Numidium after Emperor Uriel Septim asks you to find and destroy a "letter sentimental in nature", while laying Lysandus' ghost to rest becomes more or less a sidequest, despite being the initially more-significant request.
In Morrowind, you start to become the Nerevarine after you step off the boat onto Vvardenfell. What happened before then is unimportant.
You are fated to save Tamriel when you end up in the "off-limits" prison cell in Oblivion, when the Emperor commands "LET ME SEE YOUR FACE!"
What happens before the character's defining point doesn't matter, and thus isn't written into the Scrolls. In fact, more often than not, a character isn't a native of the province the game concerns itself with. In (All Hail) Morrowind, it's explicitly stated the character isn't from the titular province.
No story should require a Prologue... does anyone seriously begin play without first conceiving a background idea for a "roleplaying" character? Get to the point immediately.
Canonically, the PC accomplishes the Main Quest, and the repercussions are felt throughout the sequel. Jagar Thar was overthrown. The Mantella Crux was activated and the Illiac Bay did stabilize (among other things). Dagoth Ur was Defeated. The Tribunal was overthrown. Mehrunes Dagon's invason was spectacularly defeated, and the Ja-Kha'jay/Liminal Barrier/Lunar Lattice was repaired. And Jyggalag has returned. The next Elder Scrolls game's MQ should have similar word-shaking repercussions.
Shall I repost my idea from the first thread, with full rules?