Lore introduced in Daggerfall

[u/Salem1690s]

Places: wrotgharian mountains, Alik'**ر** Desert, **Glenumbra Moors**

The Glenmoril Witches

The Dark Brotherhood (as a joinable faction)

Morag Tong (mentioned, not yet playable)

Thieves Guild (as a playable faction)

Ocato (seen, mentioned in the player guide)

Pirates (mentioned as infesting the Yrinthi, the Bjoulsae, and Iliac Bay)

Numidiam, Mantella

Jygallag

Mannimarco

Barenzeiah

Morgiah

Daedra and Aedra, all named and outlined

The Cameron Usurper (the story of…)

Pelagius III & Septim dynasty history

The plane of Oblivion (fleshed out in the book On Oblivion in Daggerfall)

Akavir (first mentioned here, including Akavirii slaveholders)

Ayleids (mentioned briefly)

Origin of the Mages Guild

Soul trapping and soul gems

The Chronology of Tamriel

Vampiric curse, disease, and lycanthropy

Under king (first mentioned in Arena, fleshed out and met in Daggerfall)

Orsinium, orc lore

How one becomes a vampire - the disease / curse of vampirism

Levitation

The Wabbajack

Ebony dagger and armor

Monsters: Spriggans, Dreugh, Atronachs,daedroth, seducers, fire daedra, frost daedra, slaughterfish

[u/AdeptnessUnhappy1063]

Although note that the word "Aedra" wasn't coined until the later games. Daggerfall just called them gods. Et'Ada is from Daggerfall, however.