All the residents of Pell's Gate. The faction gives them all a common set of greetings and dialogue responses about Umbra as well as giving everybody access to Irroke the Wide's house.
If you tell Glarthir that people are out to get him during the Paranoia quest, but refuse to kill them yourself, they are added to this faction so that Glarthir will attack them on sight.
Resident of the Private Quarters in Leyawiin Castle. The faction doesn't actually affect the private quarters; it merely owns the two doors that lead into the underground torture chamber, most likely to stop town guards inadvertently walking into the chamber on their rounds.
Pirates on board the Marie Elena during the Dark Brotherhood quest A Watery Grave. Its members own the various decks of the ship, along with its contents.
The faction representing the player and close friends. Bendu Olo is the player, him or herself, and is renamed at the start of the game.
The faction is given explicit ownership of a number of items around the map. Many plants and ingredients found in Gottlesfont Priory are owned by the player, presumably so it appears the Sisters are aiding you. The wine, goblet and berries that Claude Maric offers to share with you in The Tiber Septim Hotel are also owned by the player.
When Jauffre unlocks his chest, ownership of it is transferred to this faction.
Prior Maborel gives you his horse by changing its ownership to this faction. The same happens to the Weynon Priory horse after the attack on the priory.
Many other factions change their relationship to this one during the course of the game.
The Mazken's reaction is set to -100 if you side with the Golden Saints during The Cold Flame of Agnon; conversely, the Aureal's reaction suffers the same penalty if you side with the Dark Seducers.SI
If the shaman of a Goblin tribe is killed, the reaction of the shaman's tribe is set to 100, although if you then kill another tribe member, the reaction is set back to 0.
After closing each city's gate during the Allies for Bruma quest, the reaction of that city's citizen faction is boosted by 20.
At the start of Malacath's quest, the reaction of the Malacath Ogre Faction faction jumps by 50 and at the end it is dropped by 50 again.
After the battle in the Imperial City, the citizen factions for the Imperial City, Chorrol, Bravil, Cheydinhal, Leyawiin, Anvil and Skingrad are boosted by 30; the factions for Bruma and Kvatch by 20, as those cities already like the player more. Additionally, the Mythic Dawn reaction is set to 0 so sleepers should no longer attack on sight.
The Oblivion gate daedra faction has its relationship set to 100 at one point during the E3 demo, then set to -80 later on.
† The Dark Minion is only present when the Vile Lairofficial download is installed.
‡ Vault Guardians are only present when the Wizard's Tower official download is installed.
You are added to this faction if you become a vampire. It seems to exist only to increase Janus Hassildor's relationship with you. You are removed again when cured.
Dar-Ma becomes a member of this faction during the quest A Shadow Over Hackdirt. Although it has no reactions itself, the HackdirtBrethren faction has a +100 reaction to it. This ensures that the Brethren won't attack Dar-Ma during her escape.
This faction contains all those who spend at least some part of their time in prison. Audens Avidius gets added when he is sent to prison at the end of Imperial Corruption and Larthjar the Laggard is removed at stage 50 of Lost Histories. You never become a member of this faction.
The residents of the Dark Brotherhood Sanctuary are added to it at the start of the Dark Brotherhood quest Purification, but there are no other references. It ensures that you won't receive a bounty or be kicked from the Dark Brotherhood for attacking the members without provocation.