The Blades are the hidden Eyes and Ears of the Septim Emperors in the provinces of Tamriel. Originally tasked with collecting far-flung fragments of Numidium, they became a prestigious service order for citizens demonstrating the greatest loyalty to the Emperor. To be named in the Blades by the Emperor is a great honor, and publicly acknowledged members serve openly in noble courts and diplomatic posts. Privately, many Blades members act as the Empire's intelligence agency. Such agents conceal themselves with secret identities, operating in disguise as couriers, observers, spies and bodyguards throughout the Empire.
The Remanada traces the history of the Blades to the original Akaviri bodyguard of Reman Cyrodiil. According to this legendary account, the same immortal Akaviri pledged themselves to Cuhlecain in order to aid General Talos' ascent to the throne. Their ancient stronghold, Cloud Ruler Temple, is located in the Jerall Mountains.
For additional general information, see the lore article on the Blades.
 The Blades in Oblivion
Jauffre is the current Grandmaster. When you first bring Brother Martin to Cloud Ruler Temple during the Weynon Priory quest, Jauffre offers to make you a member of the Blades. You can choose whether to accept the offer or decline; if you decline, you can ask Jauffre at any later time about "Join the Blades" and become a member. Jauffre will not offer you membership if his Disposition is below 40, in which case, use a Charm spell to temporarily boost his disposition. Also, Jauffre cannot offer you membership if he dies (which is possible during the quests The Defense of Bruma and Light the Dragonfires). If you want to eventually join the Blades, you may want to be sure to join before those quests or else keep Jauffre alive.
The primary advantage of joining the Blades is that you can use anything in Cloud Ruler Temple (beds, a free horse, free weapons in the Armory, books, etc). You are given an Akaviri Katana upon joining. There is no advancement in this faction, nor are there any associated quests. Although the Main Quest could be considered to be the Blades faction, it is not necessary to join the Blades to complete the main questline.
There are three total ranks in the Blades in Oblivion: Knight Sister/Brother, Captain, and Grandmaster. But only the first one is available to the player.
 Blade members in Oblivion
There are two Factions for the Blades. Blades contains most of the NPCs listed above while Character gen Blades contains Baurus, Glenroy and Captain Renault - the three you meet at the start of the game.
* These NPCs are not actually part of the Blades faction, but are included here for completeness.
- Though the Blades are an established authority in the Empire, they do not pursue the common duties of law enforcement: Blades will not arrest you if you are caught committing a crime or if you have a bounty on your head.
- The Order of Talos serves an auxiliary function for the Blades, secretly offering shelter and assistance to traveling Blades as well as providing a way for retired Blades to continue serving the Emperor in a more subdued fashion. A chapter-house of the Order, Weynon Priory, is involved in the Main Quest.