Jaciel Morgen (?b - ?d)
Nocturnal Lieutenant Jaciel Morgen is a Greater Nocturnal responsible for ruling over the Shade Perilous, a pocket realm of the Evergloam. Despite being a powerful Daedra, she is prone to bouts of debilitating melancholy, as is commonly the case with her kind. Her relation to the Daedric Prince Nocturnal is unknown.
At one time, Morgen held the precarious loyalty of the clanless Seducers. In preparation for his invasion of the Battlespire during the Imperial Simulacrum, Mehrunes Dagon allied himself with the Mazken, and the Seducers in the Shade Perilous duly entered into his service, betraying Morgen. The realm was subsequently invaded by the armies of Dagon. In their fervor to please Dagon, Shardai Clan and Xivilai's Clan conquered the realm rather than simply requesting passage, and the Shade Perilous was abandoned to be fought over between Flame Atronachs and Frost Atronachs.
Amidst this horror, Morgen's sorrow and shame at the loss of her realm drove her into deep despair. She cast her spirit into the Dreamsleeve and hid herself behind the Night Portal, which was subsequently sealed when the invaders stopped the flow of Nocturnal mana through the realm. Meanwhile, her most loyal servant Deyanira Katrece the Lesser Nocturnal blamed herself for his mistress' downfall, having pleaded the Seducers' case. Hoping to wake her from her slumber, Deyanira ordered a mortal apprentice from the Battlespire to strike her with an enchanted dagger, banishing her to the Void. The apprentice brought Morgen the dagger, and the sorrow caused by her servant's death was enough to break her from her melancholy.
Despite her initial anger, Morgen agreed to help the apprentice leave the realm and continue following Dagon's retreat. As vengeance for the invasion of her realm, Morgen aided the apprentice in a final confrontation with Dagon at his Hunting Lodge. She was able to hold off the Prince's power long enough for the apprentice to strike him with the Broadsword of the Moon Riever and banish him to the Void.
Following Imago Storm's temporary control over Clan Dagon, it is likely that the occupation of the Shade Perilous was ended, although it is unknown whether or not the Nocturnals regained control of the area.
Jagar Tharn (a.k.a. Nightingale) (?b - 3E 399)
Jagar Tharn was the Imperial Battlemage who secretly imprisoned Emperor Uriel Septim VII and used Illusion magic to masquerade as the Emperor for a decade. From 3E 389 to 3E 399, a period since known as the Imperial Simulacrum, Uriel VII was held captive in a realm of Oblivion while his battlemage reigned over the war-torn Empire. He was finally killed, and Uriel VII was freed and restored to the Ruby Throne. The Emperor dubbed the hero who accomplished this the Eternal Champion, and granted him a place by his side. It is not entirely known what Tharn's goals and personal accomplishments were during his reign.
Jakben, Earl of Imbel (a.k.a. Springheel Jak) (?b - 3E 433)
Jakben was the Earl of Imbel, a noble family dating back to the late First Era. He was born some time in the Third Era. In life, he abandoned his birthright to become a master thief, and became known as Springheel Jak. He was infected with vampirism, and used his noble status to hide his undead nature for two hundred years before finally being slain in 3E 433.
Count Janus Hassildor
Janus Hassildor, an Imperial noble, was the Count of Skingrad and an acquaintance of the Mages Guild. Most of the people in Skingrad seem to have believed that Count Hassildor was eccentric or crowd shy, but the true reason was far more disturbing however, as evidenced by his gaunt face, pronounced cheekbones, and fierce red eyes: the Count was a vampire. Although he was one himself, he disliked others of his kind, claiming that they had given in to their animal urges. Other vampires were a problem for Hassildor, as they often took up residence around Skingrad. This attracted many Vampire Hunters who often asked unwanted questions. Hassildor's wife, Rona, is also a vampire, but has not been able to come to terms with her condition and thus fell into a coma. This grieved the Count and so he enlisted the help of a stranger to find a cure for his wife. His fate is unknown, though as a vampire, he could live indefinitely.
Jastyaga (?b - ?d)
Member of the Order of Diagna who wrote of the joining the of the armies of Daggerfall and Sentinel "to hold the wicked orcs in their foul Orsinium fastness... and burn aught in cleansing flame" in 1E 950.
Grandmaster Jauffre (?b - ?d)
Secret Grandmaster of the Blades during the Oblivion Crisis. He lived undercover as a quiet monk of the Order of Talos at Weynon Priory near Chorrol. At the onset of the Crisis, he took custody of the Amulet of Kings and instigated the search for Martin Septim, the only surviving heir to the throne. Later, the priory was sacked by the Mythic Dawn. Jauffre survived and got Martin to the safety of Cloud Ruler Temple, but lost the Amulet. He helped Martin decipher the means by which to defeat Mankar Camoran, although it is unknown if he survived the remainder of the Crisis.
Jeek of the River (?b - ?d)
Jeek of the River was Captain of the Jorrvaskr during the Return. He and Ysgramor had grown up together, and the twenty-one Companions who composed his crew were Ysgramor's closest friends. Ysgramor himself gave him his name. He was the discoverer of the Skyforge, founder of Whiterun, and keeper of the original oath of the Companions, which was lost to time. While other crews sought glory in conquest, his was the first to settle and serve as protector for the settlers who followed them.
Gentleman Jim Stacey (?b - ?d)
Gentleman Jim Stacey was a Redguard who led the Thieves Guild in Morrowind in the late Third Era. Jim was a master thief himself, and is rumored to have possessed the legendary Skeleton Key. Under Jim's leadership, the Guild managed to establish itself despite resistance from older, native criminal groups, and focused on thieving only from wealthy royalty and merchants rather than the poor. Since the locals disfavored foreign organizations, he recreated the Bal Molagmer, a popular but extinct group of righteous thieves in Vvardenfell, as a subfaction of the Thieves Guild. His fate is not known; while the Fighters Guild and Camonna Tong claimed to have eliminated his organization, some suspect they actually just drove it deeper underground.
Saint Jiub (?b - 3E 433)
Saint Jiub the Eradicator is a saint of the Tribunal Temple and the New Temple. He was canonized for driving the cliff racers from the island of Vvardenfell in Morrowind. He died in 3E 433, and his soul became trapped in the Soul Cairn.
King Joile (?b - 1E 973)
Ruler of Daggerfall around 1E 973. During the Thirty-Year Siege of Orsinium, Joile led an invasion force to the Wrothgarian Mountains under the sponsorship of the Crystal Tower in High Rock. In the Annals of Daggerfall, King Joile's letter to Gaiden Shinji of the Order of Diagna says, "The orcs have been much plaguing the Wayresters and impeding traffic to the heart of the land". The date given for the letter was 1E 948, making it the earliest known written reference to Wayrest.
Queen Jolethe (?b - ?d)
Daughter of Magnus Septim and his wife, either Hellena or Utheilla, and sister of Pelagius Septim III. Following the death of her father, Pelagius ascended to the Imperial throne, and she took over his position as ruler of Solitude in 3E 145.
Jorg Helmbolg (?b - ?d)
A renowned Nordic war chief and Tongue of the First Empire of the Nords during the Conquest of Morrowind. Local legends say he slew the dragon Sahloknir near Kynesgrove.
Jorunn the Skald-King (2E 546 - ?d)
Jorunn the Skald-King was a Nordic High King born to Queen Mabjaarn Flame-Hair. The twin brother of Fildgor Strong-Prince, Jorunn grew up believing their elder sister, Nurnhilde, was fated to take the throne, and as such became a singer and did quite a bit of traveling. He showed a rare talent as a singer, highly prized among Nords, and was eventually dubbed the “Skald Prince” of Skyrim. However, his mother and sister were killed in an Akaviri invasion. He led the Nords to victory against the invaders, and took on a new life as High King of Eastern Skyrim.
Jsashe (?b - ?d)
Jsashe, also referred to as the "Witch-Queen of Whiterun", was a woman who in the Third Era maintained control of the area around High Hrothgar and Whiterun, in central Skyrim. She was the leader of that area's local witches coven, and a self-proclaimed Priestess of Lorkhan.
Prince Juilek Cyrodiil (1E ?b - 1E 2920)
Son and heir of Emperor Reman III and Empress Tavia. He was assassinated in 1E 2920. Before he died, he brought about an end to the Four-Score War against Morrowind and the Tribunal when his campaign against them finally succeeded in compromising their defenses, forcing them into negotiating a treaty.
Jurgen Windcaller, The Calm (?b - ?d)
Jurgen Windcaller, a Nord warrior who came to be called the Calm, was the most powerful Tongue of the First Era, possibly of all time. Like all great Tongues of his time, he was a war leader in the First Empire of the Nords, which was aggressively expanding across northern Tamriel. However, in 1E 416, their armies suffered an ignominious defeat at Red Mountain at the hands of the Chimer and Dwemer, and they withdrew from modern-day Morrowind. Jurgen would use the defeat as inspiration to discover the Way of the Voice and found the Greybeards.
For more information, see the lore article.