Skyrim:Esbern

Esbern, an elderly Nord conjurer, is a chronicler and agent of the Blades who has survived the investigations of the Thalmor by hiding in Riften's Ratway. Long obsessed with the foretold return of the dragon Alduin, the World-Eater, Esbern serves as your mentor, guide, and advisor. Despite this, once he learns of Paarthurnax's existence, he will demand that you slay him and will refuse you any aid until you have done so.

Esbern wears miner's clothes initially, but changes into mourner's clothes once you reach Sky Haven Temple with a pair of boots, and carries an ebony dagger and a selection of lower-class items and gold. In combat, he relies on mainly Destruction spells, and occasionally summons leveled atronachs. 

 
Spells
Esbern knows the following spells:
; Alteration: Stoneflesh
; Conjuration: Conjure Flame Atronach, Conjure Frost Atronach, Conjure Storm Atronach
; Destruction: Fireball, Firebolt, Flame Cloak
; Restoration: Fast Healing, Steadfast Ward

Related Quests








Elder Knowledge
Sometimes, when you go to talk to Esbern about finding an Elder Scroll, he can be found in the exterior courtyard of Sky Haven Temple, telling Delphine by torchlight about an ominous (and apparently prophetic) dream he used to have:

Esbern: ''"I used to dream of it. In the dream, I was standing… someplace high up… a tower, or a mountain. It was always just before dawn. The whole world was in darkness. Then came the flash of light – just on the horizon, within the clouds that mark the border between worlds. It could have been lightning, but there was no thunder. In the dream, the sense of foreboding grew, but I could never wake up. Then it came again, this time more distinct. Closer. Definitely not lightning now. It was orange – brilliant orange, the color of hearth and dawn. And a sound, too. Distinct and indistinct. Not thunder… something else. Something I should recognize, but in the dream I cannot place it. I want to leave my high place, to seek shelter. From what, I don't yet know. In the manner of dreams, I cannot escape. I'm forced to wait and watch. Then, finally, realization and horror arrive together. The orange is flame, heat. The sound a roar, a challenge in their ancient tongue. But now it's too late for escape. The dragon is upon me – fire and darkness descending like a thunderbolt. And  not just any dragon, but the Dragon – Alduin, the World-Eater, the dragon who devours both the living and the dead. And then I would wake up. And hope that it was just a dream… but know that it was not."

Skyrim Official Trailer
In The Elder Scrolls V: Skyrim - Official Trailer, Esbern says the following:

:"You should have acted. They're already here. The Elder Scrolls foretold of their return."
:"Their defeat was merely a delay … to the time after Oblivion opened … when the Sons of Skyrim would spill their own blood."
:"But no one wanted to believe — believe they even existed."
:"And when the truth finally dawns, it dawns in fire."
:"But … there's one they fear."
:"In their tongue, he is "Dovahkiin." Dragonborn!"''

Notes
If you have not started any quests involving him, he will simply open the porthole and tell you to go away, promptly closing it afterwards.
After arriving at Sky Haven Temple, Esbern can grant the Dragonslayer's Blessing which gives a 10% increased Critical Hit Chance vs. dragons for five days.
Esbern is voiced by Max von Sydow.
He can be a very useful follower. After you free him from his cell during A Cornered Rat, he will be an invincible follower, and will remain so as long as you avoid Delphine (and therefore Riverwood).
Alternatively, you can take him to Delphine and have them both follow you for two invincible followers. You may also have a regular follower with you.

Bugs
 
 
 
He can sometimes be found in Riverwood (waiting to engage in conversation with Delphine), in Riften, or traveling the road.
 
To fix this, you must unpatch your Skyrim game. It only appears on patch 1.5 and after the Alduin's Wall quest.