Unexpected Inheritance

Chester: Where'd you get all that stuff!?

Timmy: Inheritance? Internet? I inherited the internet!

—Fairly Oddparents

News of a death in the family is rarely well received, especially when its someone who cares very deeply for you. So deeply, in fact, that they have left you with a massive inheritance; but apparently not so much that they ever bother to get to meet you in person. This benevolent but reclusive relative you couldn't pick out of a police lineup (and trust us, this is something of a Plot Point) is usually an aunt or uncle, grandparent, great aunt or uncle, or related so remotely as to give a team of forensic genealogists weeks of work to find a direct connection.

The inheritance might be wads of cash, a lovely piece of land, and/or a set of family memorabilia. Depending on whether or not your relative was a benevolent Anonymous Benefactor is whether the money is tainted with the blood of innocents, the land contains a Haunted House built on an Indian Burial Ground, and whether the family memorabilia is something beneficial like an Ancestral Weapon or Protective Charm, or a higly cursed Evil Weapon or Artifact of Death.

In the middle of the road, the inheritance may be a Secret Legacy they are duty bound to follow, but which is nonetheless Blessed with Suck. Sometimes, there's a problematic condition you have to fulfill before receiving the inheritance.

One thing that tends to crop up is that the dead relative was alive all along and was pretending to be dead in order to pass on their inheritance. In these cases, the inheritor not recognizing their relative may allow them to be in close proximity by wearing little more than a Paper-Thin Disguise.

Compare Passed Over Inheritance and Game Between Heirs. In this trope, you do not have to worry about other heirs.

Examples of Unexpected Inheritance include:

Anime And Manga

Hanaukyo Maid Tai. Taro Hanaukyo inherits a vast fortune, a mansion, hundreds of maids and the position of family leader after his grandfather retires.
In a complete inversion, Princess Lover's Teppei Arima's parents, that he lives with, die and he finds out about his formerly unknown grandfather being the head of the Arima Group, which makes him now the living heir and sets off the plot.

Comic Books

There was that time Spider-Man's aunt inherited a nuclear power plant, making her a target for a supervillain who wanted to get his hands on it.
There was that time Pitheco inherited ten million bucks from an uncle (it was unexpected because he didn't know the uncle was wealthy) on the condition that he becomes a married man. When he was about to partake in the sacred vows, the executors of the will showed up to tell him that his uncle has secretly married and left a widow and three children. All Pitheco would inherit was the sum of twenty bucks (still on the marriage condition). The marriage was called off, much to Tooga's dismay.

Film

Brewster's Millions used this plot.
Running Scared (1986). Detective Costanzo's Aunt Rose dies and leaves him $40,000, which is enough to retire from the police force and buy a bar in Florida.
The 2001 version of 13 Ghosts, Cyrus kriticos bequeaths his nephew Arthur with his beautiful, glass walled house. The bad news? It's haunted by 12 ghosts, and Cyrus is manipulating Arthur into commiting suicide so his master plan to have a ghost-powered oracle machine succeed.
In King Ralph, the entire royal family dies. Ralph's a very distant illegitimate relative from America. Hilarity Ensues.
Used twice to introduce new characters in the Tremors franchise, in which Jodie and Rosalita each inherit the property of an uncle killed by monsters. The down side is that the property is in Perfection, so both nieces have to move to monster territory to take advantage of the bequest.
Elvira, Mistress of the Dark played with this trope twice. First when Elvira got a message telling her she's got an inheritance from a Grandaunt she never heard about before and second when she inherited her enemy's/Granduncle's fortune because she was his next of kin and he never made a will.
The Hudsucker Proxy: The Hero inherits controlling interest of Hudsucker Industries from Waring Hudsucker, who willed his shares of the company to whoever became the first person to replace him as the company's CEO.

Literature

The Sherlock Holmes story The Adventure of the Norwood Builder centers around a lawyer who learns he is to receive one the day before his benefactor dies, leading the police to believe that the titular builder was murdered for the inheritance.
- Similarly, The Adventure of the Solitary Cyclist centered around two men seeking to marry Holmes' client because she was the next of kin to a wealthy uncle who had no will, making her the heiress to his fortune by default.
In one of the Heralds of Valdemar books, Myste claims to have come into one of these as an excuse to get away from a group she was infiltrating, knowing that they would never go to the small town where her aged aunt allegedly lived.
"Mr. Humphreys and His Inheritance" in MR James' Ghost Stories of an Antiquary
Great Expectations. Pip receives inheritance completely out of left field, becomes rich and arrogant, finds out who his benefactor is, squanders money, gets the girl (it is implied at least), becomes less arrogant.
Harry Potter receives a huge inheritance from his parents whom he never knew, much less suspected of being filthy rich.
- Then he gets Sirius's house.
Jane Eyre inherits a large sum of money from a previously unmentioned uncle, though it's towards the end of the story.
Early on in The Cat Who series, Qwilleran inherits a huge fortune from his "Aunt Fanny." All Qwill really remembers about her is that she was a dear friend of his mother's and that he was forced to write polite letters to her as a boy, but since she had no surviving blood relatives, he's the one who receives her billions. The catch is that he has to live in Moose County for five years, but he grows to enjoy the small-town life fairly quickly.
The reader/protagonist of interactive book The Dandee Diamond Mystery didn't expect to be called for the reading of his/her uncle's will since the two of them hadn't seen each other ever since the protagonist was a little kid.
A common trope in PG Wodehouse's stories; they're often more of a curse than a blessing.
Angel Light, a novel by Andrew M. Greeley. At the reading of his uncle's will, Patrick "Toby" Tobin learns that he is the heir to an estate worth ten million dollars, but in order to collect he must 1) travel to Ireland, 2) present a letter from his late uncle to a long-estranged distant cousin of the Tobin clan with hopes of ending a long-forgotten family feud and 3) to symbolize the end of the feud, court and marry said cousin's lovely but troubled daughter Sara. And he must complete these three tasks within one month. And Sara is seriously considering becoming a nun. And an angel named Raphaella Light is bound and determined to help Toby to his happy ending.

Live Action Television

A variation occurs in The Boy Who Cried Werewolf. The family inherits a large house from their uncle in Romania, and it turns out that he was a werewolf who was using the house do experiments to find a cure for his "disease".

Musical

The early Ahrens and Flaherty (Seussical, Ragtime) musical Lucky Stiff has the protagonist inheriting $6 million from an uncle he's never met (on the condition that he takes his uncle's taxidermied corpse on a vacation to the French Riviera).

Tabletop RPG

Call of Cthulhu (tabletop game) supplement The Asylum and Other Tales, adventure "Black Devil Mountain". A PC receives a letter informing them that their brother has died and left them some property (which, by sheer coincidence, just happens to have Cthulhu Mythos activity going on nearby).
Classic Traveller Adventure 12 Secret of the Ancients. One of the PCs receives an inheritance from an uncle: a statuette which leads the party into a hunt to find an Ancient site.

Theater

The plot of the play Juno and the Paycock revolves around a poor Irish family being suddenly informed of a massive inheritance from a distant cousin, leading to them heavily spending borrowed money in the expectation of paying it back easily. It turns out that, due to the inexperience of the lawyer, the will is poorly worded, allowing dozens of distant relatives to stake a claim, rendering it worthless.

Video Games

The interactive fiction game Anchorhead has the main character's husband inherit a house as the last living relative of the Verlac family. Unfortunately for them, this is a game inspired by the works of H.P. Lovecraft, and the Verlacs turn out to have been not just a bit odd...
In Trace Memory, Ashley receives a package from her father for her 14th Birthday, after assuming he was dead since she was three. It contains the DTS, and a letter asking her to meet him on Blood Edward Island, thus setting off the plot.

Web comics

Ben inherits several rare and valuable arcade games from his great uncle, which allows him to buy Goblin Hollow.

Western Animation

Futurama episode "The Honking" has Bender inherit a mansion from his Uncle Vladimir. Along with the expected catch that he must spend at least one night there (which he wants to do before complaining about there being a catch).
- In the episode "A Fishful of Dollars" Fry is attempting to save Bender from jail by withdrawing his meager savings. He soon figures out 1000 years of interest adds up. A lot. While it is 'unexpected', it wasn't technically inherited.
The Simpsons features a couple of these:
- In "Selma's Choice" Great-Aunt Gladys dies although nobody inherits anything of any real value beyond Jub-Jub the Iguana. Instead the funeral and will serve more to spoil the trip to Duff Gardens and allow Selma to inherit an increased sense of loneliness and isolation. YAY!
- Played straight with an inversion in "Bart the Fink" when the Simpsons are required to spend the night in a supposedly haunted house (subverting the cliched plot when it turns out to be much more pleasant than their own) in order to collect the vast sum bequeathed to them by Great-Aunt Hortense. Until they find out that they missed the part where they only actually get $100 each while the rest goes to Ann Landers.
The Family Guy episode "Peter, Peter Caviar Eater" centers around Lois' Aunt Marguerite dying and the Griffins inheriting her opulant Newport manor. In a mild subversion of the typical plot Lois claims to have been fairly close to her Aunt before her death... she just never bothered to appear on the show or be mentioned in any way before or after.
The Tom and Jerry short The Million Dollar Cat has Tom receive a million dollar inheritance from an eccentric old woman, but with the condition that he forfeits the whole thing if he harms another living creature, even a mouse. Jerry takes advantage of this to abuse Tom, stopping the inevitable beating by waving the telegram in his face. In the end Tom has enough and starts beating on Jerry, remarking "Gee, I'm throwing away a million dollars...BUT I'M HAPPY!"
One episode of The Real Ghostbusters has Ray inheriting a castle in Scotland from a distant relative who he hadn't seen in years. The castle is (of course) haunted.
One Scooby Doo episode centered around a member of the gang getting an unexpected inheritance worth millions - which turned out to be millions in Confederate currency, which was worthless (clearly they never thought of selling all that Civil War memorabilia to museums or other collectors). This came up again in one of the feature-length episodes.
One Rocky and Bullwinkle episode had Bullwinkle as the heir to the Earl of Crankcase, requiring him to spend a week inside the family manor before inheriting a 1 million pound note. At the end of the week it turns out that he isn't the rightful heir after all, and the actual heirs learn to their dismay that the note is a promissory note, and that they are now obliged to repay the late Earl's debts.
- Another story arc had Bullwinkle inherit a mine from his Uncle Dewlap. The mine turned out to be in a mountain that floated miles overhead, because the mine was the only source of the anti-gravity metal Upsidasium.
While not strictly adhering to the trope (in that the deceased in question isn't a family member, but rather the leader of a rival gang), Batman: The Animated Series has one in 'Joker's Millions', in which the Joker, particularly down on his luck in terms of cash at the time, inherits $250 million from King Barlowe, a crime boss with whom he had shared a mutual hatred. As it turned out, this was all a big Thanatos/Batman Gambit on Barlowe's side, as $240 million from the fortune was counterfeit, and the IRS was knocking on Joker's door to the tune of around half the total. Barlowe correctly assumed that, by the time he'd gotten around to watching the video will, Joker would already have blown through the $10 million that was real. As such, he'd either have to go to jail for tax evasion, or admit that Barlowe had fooled him (which Barlowe had also known that he would never do).
One Punkin Puss And Mushmouse episode featured Mushmouse inheriting one million pounds from a British uncle. Punkin Puss spent most of the episode trying to be on his good graces because of the inheritance until he and Mushmouse learned it consisted not of pounds as the British currency but one million pounds of cheese.
The premise of the short-lived cartoon Monster Farm (not Rancher) involved a young man inheriting said farm from a great uncle Karloff.