The Diablo series is well known for its dark gothic atmosphere and its status as the premier loot-grinding RPG, but it also boasts a good deal of lore. Some of it is historical, detailing the world of Sanctuary and its creation, while some of it tells the story of each game and its antagonists. Throughout this lore, some characters have made their mark on the series, and would be welcome additions to upcoming Diablo 4, its details still largely unknown.
Who would be able to appear in the new game, though? It takes place many years after its predecessor Diablo 3, so returning characters would need to have unnaturally long lives, or return as spirits. Even under these conditions, there are a few characters who ought to come back. Here are ten good options, from least to most interesting.
10 Covetous Shen
"The Jeweler" from Diablo 3, Shen provides basic gem-related services to the player such as the crafting of gems and jewelry. Lore-wise, however, Shen's true nature is a mystery. He appears as an old man hiding in a barrel, but quickly turns his misfortune into gain as his captor sets off a curse that would have prevented Shen from finding the treasure he was hunting.
He also has a great knowledge of culture, and has shared experiences with Deckard Cain. Some characters imply that Shen may be a god in disguise. If so, it's very possible for Shen to appear in Sanctuary's future.
9 Abd Al-Hazir
A scholar, who pens many of the enemy descriptions in Diablo 3. He comes across as the reverse of Deckard Cain: a book-smart researcher whose lack of experience keeps him from being especially useful.
His inaccurate reports bring a breath of levity to an extremely grim world. Despite his prevalence in the in-game journals, the man himself only has a minor appearance in person. It might be fun to spend more time with him, if he or his spirit manage to survive until Diablo 4.
8 Adria
First appearing as a helpful vendor in the first game, she returns as an antagonist in 3, sacrificing her own daughter to spur the return of Diablo. Although little is known about her life in Tristram, the shift still comes as something of a shock. Stranger still, the journals containing her final thoughts paint a human picture of a thoughtful woman with tough questions to ask of the world.
What drove Adria to commit such heinous acts? If some part of her survives, it would be interesting to hear more in Diablo 4. We may find answers sooner than that, even, since she is set to appear in the upcoming Diablo Immortal.
7 Kormac, The Templar
One of the three supporting characters who can accompany the player in Diablo 3. Hailing from an order of religious warriors, Kormac begins the game as an uncompromising zealot, and ends the game by dismantling his former order. Compared to the other two followers, Kormac's story is the most dramatic.
What do the Templars look like years in the future, when Diablo 4 takes place? Would Kormac have reformed it, bringing it new purpose, or would he have stamped it out entirely? Most importantly, does he ever get with his crush Eirena? These are questions that need answers.
6 Tyrael
An angel and long-standing player ally. First introduced as a major figure in Diablo 2, Tyrael provides guidance on matters of Heaven and Hell. In 3, he sheds part of his divinity to become mortal, appearing as human while continuing to serve in Heaven.
His central standing in Diablo lore, along with the fact that he survived all three games, practically guarantees his return in Diablo 4. However, it remains to be seen whether a mortal angel would suffer from old age, which could kill him before the events of the next game begin. Hopefully he makes it, as it would be interesting to see how his dramatically changed life has gone.
5 Marius
The narrator of Diablo 2. Never appearing in-game, Marius is used by the Prime Evils to cause many of the main crises throughout the game, and then killed. Even for Diablo, Marius' fate is particularly dire, but despite his death, he's not wholly forgotten: he appears in 3 as a part of Tyrael's memory, representing one of the angel's regrets.
It may be a long shot, but it would be nice to give Marius some relief after all he was subjected to, as long as his soul can still be found after all these years.
4 Li-Ming, The Wizard
One of the seven playable classes in Diablo 3. Li-Ming is already a little more interesting than the other heroes, since their motivation is based on heroism, while Li-Ming is focused on self-advancement. It's fun to play as a stuck-up jerk, but this personality could also spell trouble for the world of Sanctuary.
Throughout the series, mages have a tendency to go mad with power. Villain Zultan Kulle is a good example, as is the Sorcerer class from the first Diablo, who appears in 2 as an enemy. What would the Wizard be like years after the events of Diablo 3, having attained the unimaginable power she was seeking?
3 Imperius
Current leader of the Angiris Council, and considered one of the greatest warriors in the Diablo universe. His role in Diablo 3 tends to be hostile, and he was about to attack the player before being interrupted by Diablo. He requests the players' aid later, but offers no gratitude.
Altogether, Imperius is an unpleasant angel, so it's unfortunate he never appeared as a boss encounter; a battle against "the greatest warrior in all of creation" would make a good fight. Hopefully players will get their shot at him in Diablo 4.
2 Zultan Kulle
The dark Horadrim, a more sinister version of Deckard Cain. He appears in Act 2 of Diablo 3 as an evil wizard requiring resurrection to allow the player access to his archive, and the Black Soulstone.
Despite being an extremely straightforward one-off antagonist, he is fondly regarded by the playerbase for his unapologetic villainy and entertaining banter, which may be why Blizzard brought him back as part of their expansion content. He currently exists as an artificial simulacrum of himself, making it simple enough for him to exist years in the future, when Diablo 4 takes place.
1 Deckard Cain
The last Horadrim, best known as an old man who stands in the middle of town and identifies magic items. He has appeared in every Diablo as a major character, and in many ways he represents the soul of the whole series. His narration brings to mind dark histories with foul roots stretching into the present, and his familiar greeting, "stay a while, and listen," is the most well-known quote in the series.
Unfortunately, he was killed in Diablo 3, but it's still possible for him to make an appearance in 4, either in spirit form or as narrator of collectable lore items as he was in 3. It's hard to imagine a Diablo without him, but perhaps he's earned his rest.