Annalise is believed to be the last remaining member of Cainhurst royalty and is the ruler of the Vilebloods, a faction of Hunters that oppose the Healing Church. Annalise's chambers are hidden behind an illusion, which is guarded by the undead Martyr Logarius, leader of the Executioners that exist to hunt Vilebloods. If players beat the Logarius boss and then wear his Crown of Illusions, the path to Annalise will reveal itself.
There is a key item called Cainhurst Summons in Annalise's chambers. If these are given to Alfred the Executioner then he will head to her chambers and beat Annalise into a literal pulp of blood and flesh; because of her immortality she is still technically alive, hence Alfred's thorough assault to make sure she's otherwise incapacitated. Examining the remains will give players the Lump of Flesh item, which can be used to revive Queen Annalise at the Altar of Despair after beating Ebrietas, Daughter of the Cosmos.
Annalise is the leader of the Vilebloods covenant in Bloodborne, which focusses on PvP. Joining the Vilebloods will gift players with the 'Respect' gesture, the Vileblood Oath rune, and the Cainhurst Badge, which will add the Chikage katana weapon and Cainhurst armor set to the store in Hunter's Dream. While equipped with the Vileblood Oath rune, any Hunters that are killed--both NPC and player alike--will reward the player with a blood dreg, which can be given to Annalise. Giving one blood dreg will reward players with the 'Deep Respect' gesture, however all blood dregs from then on merely serve the leaderboards of how many blood dregs the player has accumulated overall. The Vileblood Register item that can be found in Cainhurst Castle allows players access to browse the Vileblood leaderboards.
Players can also choose to 'kill' Annalise as well. Upon doing enough damage she will slump to the floor in agony; leaving and returning the area will show her in the same gory state as when Alfred would massacre her. Choosing to attack Annalise has no effect on Alfred's questline and he will still celebrate with the same dialogue stating he's beaten the Vileblood Queen. Whence revived players can still once again begin submitting blood dregs to the Queen.