The Dragonborn is sent to recruit the old Blades scholar by Delphine, the other living Blade during the Fourth Era. Esbern is living in the Ratways beneath Riften, where other vagrants know him as a crazy, paranoid old man.
Once the Dragonborn, Delphine and Esbern successfully establish Sky Haven Temple as a new base of operations for the Blades, the player character will be able to assist Delphine in recruiting up to three Followers as new Blades members. At this point, Esbern will point the player character to Dragon Hunts which the Blades recruits can participate in.
Esbern can also grant the Dragonborn with the Dragonslayer's Blessing, which gives a 10 percent bonus chance to deal critical damage against dragons for five in-game days.
After the Dragonborn slays enough dragons, Esbern will ask the player character for a Dragon Scale and Dragon Bone to produce a special potion that grants the Dragon Infusion perk which permanently reduces melee damage from dragons by 25 percent, very useful on higher difficulty levels!
In the game, Esbern is voiced by Max von Sydow.