This man/woman/creature is a One-Man Army, they have killed countless people, their power and skill are known throughout the world... Only that happened a while in the past, and by now they're dead.
This trope is about badass characters who are discussed by the cast sometimes, sometimes stories are told about him, frequently flashbacks are included in visual media. However, this character has been dead since before the series began. This character is frequently a family member of one of the main protagonists or villains, a mentor who taught the good guys and/or bad guys everything they know, a legendary figure from ages past, or sometimes all 3, but whether it be from old age, battle, or other cause, this character is dead prior to the story. By definition this character can usually only be referred to by someone else or appear in flashbacks, but never actually appear, however if the story has time travel in its repertoire this character can sometimes appear physically in the story, but that is pretty rare.
If the character is dead and brought back to life at some point, that's Back from the Dead, which invalidates this trope if said person remains alive for some time, but it's only fairly briefly it still applies. If this character is believed by most everyone to be dead but turns out to not be, that's Not Quite Dead. If this character dies, goes to the afterlife and fights their way out, that's Escaped from Hell. If this character is defeated, but not killed and instead sealed away, that's Sealed Badass in a Can. If they are prophecised to return someday, that's King in the Mountain. If this character dies during the actual story, no matter how early, then it is Square Peg, Round Trope. If the character is brought back as an undead to assist the heroes, that's Cavalry of the Dead. This character is sometimes the motivation for a Roaring Rampage of Revenge, sometimes the character is someone the main characters aspire to be, maybe being that MC's Can't Catch Up. Unlike Famed in Story, this character doesn't actually HAVE to be famous, just important enough to the to one or more of the main characters to be mentioned sometimes. Frequently the inverse of Living Legend. A type of Posthumous Character.
This is a death trope, unmarked spoilers ahead.
- In the Anime version of AKIRA, the people searching for the eponymous character eventually discover he has been Dead All Along, leading to a Downer Ending.
- In Inuyasha the title character's father is a demon lord said to have been one of the most powerful demons of his time, both of his sons aspire to be as strong or stronger than he is, and many plot points throughout the series occur because of machinations he set in motion prior to his death. However, he ends up dying from his injuries fighting Ryūkotsusei, a dragonlike demon.
- Lyrical Nanoha has the last Sankt Kaiser, the Queen deemed second to none in combat who sacrificed herself to stop the Ancient Belka War, an act that led to her being worshiped as a Christ-like figure in The Multiverse. Nanoha in her Super Mode could barely keep up with an untrained clone of hers during the climax of Magical Girl Lyrical Nanoha StrikerS, and flashbacks in Magical Girl Lyrical Nanoha ViVid shows her curb-stomping other powerful legendary figures from her time.
- Moribito: Guardian of the Spirit has Jiguro, a spear-wielding badass who trained Balsa. He dies of an illness a few years prior to the story.
- Hashirama Senju is the man that shaped the current existing shinobi system and ended years of conflict, something that was thought to be impossible during his time. Not to mention he can squash Bijuus flat if he feels like it.
- The Second and Fourth Hokage all fit for this trope, to about equal amounts.
- Madara Uchiha was a contemporary and rival of Hashirama, revered as the most powerful Uchiha ever. Hashirama killed him in a duel that carved a canyon into the surface of the planet. However, Madara resurrected himself with Izanagi and managed to live until 12 years before the start of the series, when old age finally caught up to him. Before dying, he passed his name and legacy on to Obito Uchiha, and was later brought back as a zombie by Kabuto and briefly managed to fully resurrect himself, but died a third and final time after having the Ten Tailed Beast extracted from him.
- One Piece has the King of the Pirates Gold Roger, over twenty years dead. Only the World's Strongest Man, Whitebeard, was said to ever fight on equal terms with him. One of the big secrets surrounding Roger's capture and execution is the fact that he was never actually captured, Roger surrendered and used his death to spark the Great Pirate Era.
- In the first few issues of Savage Dragon, the hero known as Mighty Man had been dead for a few weeks. He shows up later in the series. Or at least, one of him does.
- Wonder Woman (1987): Diana's aunt Antiope has been dead for centuries, but once led the contingent of Amazons who were furious at the gods for punishing them for fighting against Hercules and his men for drugging and raping them and founded the Bana tribe of Amazons from which Artemis hails.
- Assassin's Creed (2016): Aguilar died 490 years before Callum Lynch was put in the Animus. Due to the ability of the Animus, Callum and the audience get to see how badass he was when alive.
- The Star Wars Expanded Universe has enough examples to take up its own page, many of which later appear alive in EU material, either as main characters or adversaries.
- The series (most notably Jingo) makes frequent mentions of Tacticus, an ancient Morporkian general who was renowned for his military expertise to the point that the word "tactic" was coined in his honor. He was unique among Morporkian generals in that he actually cared more about winning battles and keeping his men alive than "glory" measured by how many people died on either side.
- Sam Vimes' ancestor "Stoneface" is another example
- Averted, inverted and played with in the form of Cohen the Barbarian, the veteran hero who (especially in earlier appearances) is a hero who has outlived his time... but is still alive.
- J. R. R. Tolkien has dwarfs routinely cite their ancestors. In particular, Thorin Oakenshield mentions Thráin, King Under The Mountain during the pilgrimage to Lonely Mountain in The Hobbit. Thráin is said to have routed the dragons in the area, and amassed a huge treasure horde in his mountain's caverns.
- In James Clavell's Noble House, tales of Tess "Hag" Struan's long, cunning, and ruthless rule-behind-the-throne through successive tai-pans (chief executives) of Struan's Trading Company, and her dealings with hers and the company's enemies, were commonly discussed by the main characters, some perhaps embellished a bit. They were definitely in awed respect for her legacy though. Clavell's previous novel Tai Pan, set over a century before when the company was founded after the British purchase of Hong Kong Island, did depict her rise to power and influence as a younger lady and showed that there was probably a lot of truth to those later tales, though.
- A whole heap in A Song of Ice and Fire. Notably, Rhaegar Targaryen, Arthur Dayne, Gerold Hightower. Brandon Stark probably qualifies, too. Aemon Targaryen The Dragon Knight is widely viewed as the greatest Kingsguard and finest knight to ever live.
- Warhammer is full of undead, but Lord Kroak, Slaan Mage-Priest of the Lizardmen, is a straight example: one of the oldest beings on the planet, he died several thousands of years ago defending his doomed city, using his last seconds to cast a spell so powerful it leveled the city and killed every demon miles around, and has remained dead since then, even though the Warhammer setting has a tendency to have people come back to life in various states. His corpse remains extremely magic and is taken into battle by the Lizardmen because the sheer magic power emanating from his remains is a huge death-sphere centered on him, which spares only Lizardmen.
- Warhammer 40,000 has its own examples (Generally in the form of Space Marine Dreadnoughts, near-dead Marines in a life-support coffin in a giant robot). A notable example is Bjorn the Fell-Handed, who fought alongside the original Space Wolves, 10,000 years before the events of 'present Warhammer 40K', and died in battle. He infrequently gets called back from lifelessness to fight for the Wolves.
- Generally subverted, as having 10,000 years of lore explored over decades means that often the 'long dead' badasses will get flashback works, but for ones that fit it straight? Macharius, essentially Alexander the Great and Sun Tzu's child, Horus on the villain side, the God-Emperor himself probably qualifies, the entire cast of Horus Heresy is basically exploring these guys. The Primarchs, though they're usually not dead proper, but until recently did not appear. (With Ferrus Mannus being the straightest example, along with Rogel Dorn).
- This comes up throughout Assassin's Creed, both in individual games and just by the fact that the games are usually set centuries apart from each other (or just several decades for the more recent games). Assassin's Creed II, set in Renaissance Italy, directly addresses the previous player character, who lived in Syria during the Third Crusade, and Altaïr himself is a Long Dead Badass to pretty much any installment set after the Crusades. Ezio becomes one to the next protagonist, Connor Kenway, who along with Shay, Haytham, Arno becomes one to the Jacob and Evie Frye in Syndicate, with Connor's grandfather Edward and his quartermaster Adéwalé being between Connor and Ezio. Internally, Captain Kidd is a Long Dead Badass to Connor, and unlike these other characters never physically appears. To top it all off, just about every single character in the entire franchise is a Long Dead Badass to the characters in the present-day Framing Device, especially Desmond Miles, who is descended from most if not all of the player characters.
- Chrono Trigger. Cyrus was Glenn's AKA Frog's best friend and Knight Captain of Guardia, who's sword skills are second only to Frog's own. He dies fighting Magus, sacrificing himself so that Glenn could escape some years before the middle age time period begins. He also appears briefly as an apparition during one of the game's sidequests.
- Dante's father, the demon Sparda, is dead by the time the Devil May Cry games take place. He's renowned for rebelling against his demon kin and saving humanity from them. Dante has taken up his legacy. Interestingly, the series never states exactly how he died, and the only place where he's directly confirmed as dead is in the prologue of the first game.
- The Elder Scrolls:
- There are countless in the series' backstory. Pelinal Whitestrake, Wulfharth Ash-King, Ysgramor, Reman Cyrodiil, Tiber Septim, Uriel Septim V...and that's just naming the Imperial and Nord examples. More details about them (and more) can be found on the franchise's Historical Figures character page.
- To the Dunmer people, most prominently shown in Morrowind, Indorial Nerevar is this. He is the Founder of the Kingdom and the Tribunal rule in his name (though they may very well be responsible for his death). He's been sainted by their church and is held up as the standard all Dunmer should aspire to be.
- The Khajiiti people have one in Rajhin, the legendary Impossible Thief who is credited with, among other things, stealing the Ring of Khajiiti off the arm of the Daedric Prince Mephala, stealing a tattoo off the neck of the sleeping Empress, and stealing the entire city of Falinesti. A beloved thief, however badass, may seem strange to an outsider, but to the Khajiit (who are a very pragmatic race with no word for "rules" in their language), it is quite justified. In modern times, Rajhin is considered the God of Thievery to the Khajiit.
- In Skyrim, the three First Tongues trained on how to use the Thu'um by the repentant dragon Paarthurnax, by the time the game rolls around. Gormlaith, Felldir, and Hakon are referred to by Paarthurnax as "wuth fadonne", or "old friends"; for an ageless dragon like Paarthurnax to refer to them like that shows how much they meant to him.
- The Vault Dweller from Fallout. At the very least, he was 16 by the time fallout started in 2161. He defeated several gangs, and even a Super Mutant army. 120 years later, by the time of Fallout: New Vegas (2281), he's probably dead (unless he had been ghoulified at some point), as he would be 136 years old at the very least, but his status as a legend still holds. He appears in the much reviled Fallout: Brotherhood of Steel where the player can kill him in an optional sidequest in the game's second act, despite them being on the same side earlier.
- The Champions in The Legend of Zelda: Breath of the Wild were four warriors chosen from their various races to pilot the Divine Beasts based on their preexisting skills in combat. They were killed in the Great Calamity when Ganon took over the Divine Beasts with his evil essence, and a century later people both praise their deeds and lament their deaths (especially the Zora princess Mipha, due to her people being Long-Lived and personally remembering her from back then). Link and Zelda are assumed to be this, but both are actually still alive through supernatural means.
- Suikoden III has the Flame Champion.
- Played for Laughs in Tales of Monkey Island. Guybrush finds himself trapped in a whale along with an inept crew of pirates. The exception is Santino, a real man among men, a guy whose innumerable talents would be invaluable in getting out of the situation. Of course, he's been dead long before Guybrush got there.