Will

I, the undersigned, being of sound mind, do hereby bequeath ...
Wills combine death and the prospect of riches, making them potent plot devices. People will commit crimes to get in the will, or comply with bizarre conditions, but some are lucky enough to receive a massive inheritance out of the blue.

Writing the will
The fun starts before the will writer's death, with the decision about who gets what. Since they can keep changing their mind, there is ample opportunity for coercion, both by them and of them, and there may be several versions of the will floating around.

If the will writer is a jerk, or worse, they'll use the threat of being cut out of the will to control the prospective heirs. 'Do as you're told, or you'll be out on the street without a penny to your name.' In the worst case, the children will be reduced to virtual slaves. The relatives may snap and kill the will writer, or they may suffer in silence, but either way, the will writer often has the last laugh, leaving their entire fortune to an ironic charity.

Just as often, the prospective heirs will try anything to get in the will. The ethical simply treat their rich uncle with extra kindness, visiting regularly and naming children after him, but draw the line at openly asking to be in the will. The less ethical may go as far as marrying the will writer, despite a multi-decade age gap - not illegal, but much frowned upon.

Crooks go further. Crooked lawyers, and other advisers, may insert small print in the will, or whole extra pages, so that will writer doesn't sign what they thought they were signing. If they can't tamper with the actual will, they may just forge one outright. Less subtle villains will use overt coercion to dictate the will, possibly even at gunpoint.

Once they're in the will, the villain then usually kills the will writer, before they can revoke the will. A Black Widow specialises in this crime.

Finding the will.
Sometimes, everyone knows where the will is, and they can get straight on with reading it. Other time, it is hidden, accidentally or on purpose. It might have been posted to Outer Mongolia by mistake, or it might have been hidden to keep the villains from realising that the will in their favour had been revoked. There is usually a deadline the will has to be found by.

If the plot is about the hunt for the will, it's a McGuffin will.

Reading the will
Traditionally, everyone involved gathered in the lawyer's office, and listened to the will being read out, but these days video wills are increasingly common. Small bequests come first, with the most dramatic revelations at the end. Either way, it gives the dearly departed a chance to speak from beyond the grave.

Snarking at the relatives is popular, along with ironic bequests. Greedy heirs will have their faults listed, before being left two pence, and something they've no use for. Alternately, they may be left the fortune, On One Condition. Jerkish will writers impose demeaning conditions; benign will writers try to correct their heir's faults. And sometimes, they could be left with nothing at all.

Sometimes, the bequests aren't what they seem. If the will writer was hiding their real fortune from the authorities, they may leave their favourite heir some minor item, with a Treasure Map hidden inside. In Speculative Fiction, odd bequests often turn out to be Phlebotinum. That worthless old tin mug might actually be the holy grail. This is one way of getting the protagonist inside the Masquerade.

The will is also a popular time to reveal unknown relations - illegitimate children, secret adoptions, siblings who have been missing for fifty years. If there was a murder, these people are now suspects. If they're not at the will reading, they'll need to be tracked down. This can also provide a Deus Ex Machina; the protagonist inherits from a distant relative they've never heard of, just when it's most convenient.

Sometimes the inheritance doesn't always go to who people think it is going to go to. Often times the Inadequate Inheritors will have their share of the fortune given to an unknown relative, a stranger, or even a favorite pet.

For the most part, the reading of the will is a case of Artistic License: Law, rather than Truth in Television. In Real Life, the only people who actually see the will (after death) are the lawyer, the executor/administrator/commissioner of the estate, and the probate court. A beneficiary does have the right to see the will, but he must specifically request it.

Challenging the will
There are various ways of getting a will thrown out. The disappointed heir could look for a later will, which means going back to finding the will.

If the will writer was killed, their murderer is automatically disinherited. The heir just has to prove they did it, setting up a Murder Mystery. Forgery and tampering are subtler crimes, so are usually left to the more cerebral mysteries.

If the villain simply had undue influence on the will writer, such as a Black Widow, or if the will is unreasonable, the only option is to take it to court. Many of the more bizarre conditions would be thrown out if they were challenged, but these cases are notoriously slow, so are seldom the main focus of a plot.

Examples:

Advertising

 * This commercial for DirecTV. Well, at least Chauncey won't have to pay inheritance taxes.

Anime and Manga

 * In one case from Detective Conan, the family of Yukiko's childhood friend comes together at the family estate to hear the reading of the deceased patriarch's will. Things are tense (aside from the inevitable murder) thanks to the arrival of an uncle who nobody had seen since he moved to Brazil 30 years ago--they think he's an imposter aiming to collect some of the inheritance.

Comedy

 * The Frantics' sketch "Last Will and Temperament": "To Jenny, I leave...a boot to the head!"
 * Within the Ace Attorney fandom, a remix using characters from the series is quite popular.

Film

 * Who Framed Roger Rabbit? has Marvin Acme's will, which was hidden. (In plain sight, as a matter of fact.)
 * Greedy is pretty much entirely about the second and third paragraphs under Writing the Will, above.
 * The Ultimate Gift uses a will at the beginning of the film to set up the story. The protagonist has to perform the convoluted tasks set forth in the will in order to inherit billions.
 * Dark and Stormy Night plays this to the hilt as the set piece. Complete with and Old Dark House.
 * The film adaptation of The Borrowers involves an unscrupulous lawyer claiming that the deceased in question never wrote a proper will, thus making him the sole beneficiary of her estate including the house that her niece's family — the film's protagonists — are currently living in. In reality, she had an extra copy hidden in the walls of the house itself because she never did trust lawyers.
 * Mousehunt kicks off with the protagonists' father leaving them his string factory and an old repossessed house that turns out to be (A) the work of a famous architect and (B) inhabited by the eponymous mouse.

Jokes

 * A doctor asked his elderly patient about what his relatives think about his hearing aides. The patient answered that he hasn't told any of them about it and that he had changed his will three times ever since then.

Literature

 * Charles Dickens's Bleak House revolves around a long-running legal case over a will. How long-running? Entire generations of descendants of the original litigants have been born, lived, and died before the novel begins. We never learn what the dispute originally was, by the time of the novel nobody remembers what it was, and the ultimate conclusion is that legal costs have consumed the entire estate, so nobody gets anything.
 * The Lord of the Rings - when Bilbo leaves the Shire, his last letter has all the characteristics of a will, including pointed comments about his relatives.
 * Several Lord Peter Wimsey plots involve wills:
 * When a will is discovered in a book Lord Peter deduces, from the water stains on the book but not the will, that one of the heirs had hidden it there to keep the condition from being fulfilled.
 * In order to find one will, Lord Peter and his client have to solve a crossword puzzle.
 * In The Piscatorial Farce of the Stolen Stomach, the odd bequest is Great-Uncle Joseph's stomach,.
 * Stephen King wrote a Sherlock Holmes story where the Asshole Victim used his will to dominate his family.
 * Several wills are plot points in the Harry Potter series--it seems like whenever Harry loses a friend or relative, they leave him Phlebotinum.
 * Sirius Black, Harry's godfather leaves him his entire estate.
 * Dumbledore leaves Harry, Ron and Hermione specific items in his will, (they're carefully considered Plot Coupons for his big Thanatos Gambit.)
 * Whether Harry's parents had wills is unknown, but he does inherit both of their entire estates as well -- assuming the Wizarding world works the same way the real world does, it's reasonable that any belongings which were not destroyed or left in the care of someone else with instructions about its disposal were sold and the money from the sale added to their account at Gringott's.
 * The Westing Game involves a man leaving his will in the form of a convoluted game, the winner of which will become his heir.
 * In L. M. Montgomery's A Tangled Web eccentric Aunt Becky willed that the name of the heir of a priceless heirloom will only be disclosed a year after her death. Because the will dropped a few hints that a unknown judge would be selecting the heir, the family members spent the rest of the year trying their best to live up to what Aunt Becky would have wanted in an attempt to win the heirloom.
 * In the Sherlock Holmes story The Case of the Norwich Builder, a will is the means of framing a young man for murder. The writer of the will leaves his entire estate to the young man, then fakes his death, leaving the young man the only suspect.
 * Quite a few of Rex Stout's Nero Wolfe novellas and novels revolve around wills; real, fake, hidden, disputed, and lost. Among them are The Red Box, Where There's A Will, The Rubber Band, When A Man Murders and Window For Death.
 * Rex Stout also uses a will in Red Threads an non-Wolfe novel.
 * In The Gates of Sleep (from Mercedes Lackey's Elemental Masters series), Marina's parents specifically name their friends as Marina's guardians should anything happen to them. Unfortunately, the will is stolen and destroyed by her aunt, letting that aunt grab control of Marina's estate and person.
 * One of Kim Newman's horror stories, "The Cold Stark House", has a particularly nasty version of the jerkass dying guy trope: it turns out in the end that the dying guy enjoys making his relations dance for the inheritance so much that he's done a Deal with the Devil to make himself and them immortal, and they've now been scheming and back-stabbing for centuries, with no end in sight.
 * In George Eliot's Middlemarch, Casaubon tries to control Dorothea Brooke from beyond the grave by means of a particularly nasty codicil, which
 * There's some comic foreshadowing of Casaubon's manipulativeness in Mr. Featherstone's will.
 * Keys to the Kingdom involves the Will of the Architect of Creation, which can bestow great power.
 * It is also sentient.
 * Several Agatha Christie stories revolved around hidden wills, and a series of cryptic clues that force the potential heirs to enlist the help of one of her detective characters.
 * A major plot point in Washington Square: Catherine Sloper already receives $10,000 yearly from her mother's estate, and by default she is going at get an additional $30,000 after her father's death. Dr. Sloper already considers Catherine an Inadequate Inheritor, and makes it very clear to her that if she marries Morris Townsend, he will change his will to completely disinherit her and donate his money to various organizations.
 * Parodied in The Will of Don Quixote, by Hungarian poet Domokos Szilágyi. It starts with the traditional opening formula of a will, but the rest is actually a list of nouns arranged in alphabetic order, with little to no relation to each other.
 * In the interactive book The Dandee Diamond Mystery, the reader/protagonist's rich and eccentric uncle left the Dandee Diamond to the one who most deserves it. However, before they can figure out who deserves it the most, they must find the diamond and the uncle's only clue in the will was talking to his parrot.
 * The Discworld book Making Money sees Moist von Lipwig left a dog by the owner of Ankh-Morpork's bank... a dog that, in turn, was left the bank. And along with the dog is a warning that if Moist doesn't care for the dog, or if the dog dies prematurely, the Guild of Assassins will come for his head. (This is a good thing for Moist, in fact, since his having a contigent contract on his life means that the Guild won't accept another one from the late owner's greedy relatives.)

Live Action TV

 * A prank on the hidden camera show Scare Tactics involved the victim being told by a man she was hired to take care of that he'd been brought back to life by his greedy heirs while they were searching for his will. The man asked the victim what her name was, then scribbled it down onto his will, claiming to leave his entire fortune to her. The greedy heirs find out--Hilarity (and terror for the victim) Ensued.
 * In Star Trek: Enterprise just before the crew is set to go into a very dangerous mission we find Dr. Phlox doing a very long and lengthy will to his extended family. He explains that he enjoys the thought of his friends and family getting something pleasurable and remembering him after he's gone.
 * In an episode of Married... with Children, Al Bundy's Uncle Stymie, the only male Bundy to be a success in life (Al credits this to the fact Stymie was the only one who never married), left his $500,000 estate to the first male Bundy to have a legitimate son named after him. Considering that the lawyer who read the will would later marry a male Bundy and give birth to Stymie Junior to get the money, Al and the other Bundys who didn't get the money even though could have challenged the will under claims of undue influence.
 * In The Dukes of Hazzard two-part episode "10 Million Dollar Sheriff", Rosco Coltrane believed he'd inherit ten million dollars from his uncle but it was later revealed that will was inaccurate and Rosco only inherited ten dollars.
 * Mash: During a posting to an aid station at the front Hawkeye makes out a will. One of the soldiers who works there says he's seen lots of guys do that.
 * An earlier episode has Frank Burns, delirious with a high fever, thinking he's going to die and dictating his will to Father Mulcahy. Among other things, he leaves "all profits from my prescription kickbacks" to his children and his clothes to Margaret Houlihan.

Radio

 * One episode of BBC radio comedy The Burkiss Way featured the reading of the will of a Lord Hackingbottmo. The will begins with a long list of people who have been left nothing, in increasingly elaborate language ("...nil pennies; the zero sum..."). This is followed by a list of people who have been left vaguely described but clearly unpleasant things ("...a rather nasty substance...something not nice in any way shape or form - and a four year supply of refills..."). An attempt to find someone who has been left something nice then turns the reading into a performance of Chattanooga Choo-choo. This is disrupted by someone finally pointing out that Lord Hackingbottmo is the person reading the will out in the first place.

Tabletop Games

 * In Shadowrun, upon the death of the Great Dragon Dunkelzahn, his entire hoard was divided in the most ridiculously convoluted will in history, with bequests ranging from the practical to the symbolic to the absurd (including the largest bequest: over thirteen billion dollars to repay the one gold coin, "accounting for inflation and interest," that Art Dankwalther's ancestor had lent Dunkelzahn in the Fourth Age). It was so extreme that a Mega Corp, the Draco Foundation, was set up just to manage the will. All of this, of course, was related to the dragon's monumental Gambit Roulette to prepare the world to defeat the Horrors when they showed up again.
 * For the curious, the entire will (minus some in-universe legal BS), plus some out-of-game annotations, can be found here.
 * Be warned: It's long -- 'Print Preview' in Firefox shows 62 pages.

Video Games

 * In the Infocom game Deadline, one major scheduled event is the reading of the will, at noon.
 * In the supplemental material for Team Fortress 2, it is revealed that the driving force behind the Excuse Plot is the last will and testament of Zepheniah Mann, arms manufacturer and proud owner of a continent worth of useless land and half the diseases known to man, the latter two caused by his layabout, brain defective sons, Blutarch and Redmond. He leaves his arms company and personal estate to his personal tracker and nurse, respectively, and his sons get the crap land and a litany of insults.

Western Animation

 * At least one Tom and Jerry cartoon has Tom inheriting a great deal of money thanks to an eccentric owner, on the condition that he forfeits it all if he harms any living creature, even a mouse. Jerry then proceeds to be a total Jerkass throughout the cartoon, taking advantage of Tom and waving the telegram in his face to protect himself. Eventually Tom has enough and says "Gee, I'm giving up a million dollars...BUT I'M HAPPY!!" and finally giving Jerry the beating he deserves.
 * In another Tom and Jerry cartoon, Jerry wrote a will leaving Tom a custard pie. Eager to claim that inheritance, Tom happily yelled: "Lemme have it!" and the pie was thrown at his face.
 * In yet another one, Tom was so sure Spike would maul him to death he wrote a will leaving everything to charity.
 * In Chip 'N Dale Rescue Rangers episode "Pound of the Baskervilles", Lord Baskerville left his mansion to his second son, who must find the will to prove it, before the first son finds and destroys it.
 * A flashback episode of "Pound Puppies" shows that, in order to keep Katrina Stoneheart from inheriting her aunt's Puppy Pound, the puppies needed to find her aunt's will, where it was stated the pound must go to Katrina's niece Holly.