Note: Major spoiler's for last night's episode of Game of Thrones below.
First of all, we don't know that Tywin Lannister is, in fact, dead. Game of Thrones is one of those shows where you really can't be completely certain that someone is dead unless you actually see the life go from their eyes (and even then, there's a chance they'll be coming back in one form or another). But if the patriarch of the Lannister family is dead, we do know who was responsible. Tyrion Lannister was ridiculed, harassed and imprisoned by his spiteful father, but he ultimately had his revenge, using a weapon that once belonged to a different, much younger (but no less sadistic) Lannister who had also ridiculed, harassed and attempted to murder Tyrion.
Tyrion's deed has plenty of precedent, not only in fiction but also in history (a favorite primary source for A Song of Ice and Fire author George R.R. Martin). Here are six of the most famous of those incidents:
1. Oedipus and Laius
Okay, so this one isn't precisely historical, but it's certainly the the most infamous example of (unwitting) patricide. As the legend goes, a prophecy predicted that Oedipus would grow up to murder his father and marry his mother. Understandably, his father, Laius — king of Thebes — wasn't particularly keen on the idea, so he left baby Oedipus on a mountain to die. Before that could happen, however, Oedipus was discovered and later raised ultimately raised by a different Greek king (Greece had a LOT of mythical kings, one for each city-state, back in the day): Polybus and his wife, Merope.
As he came of age, Oedipus went to the oracle at Delphi, discovered the prophecy and vowed to due everything in his power to prevent it from coming true. Trouble was, Oedipus didn't know that Polybus and Merope weren't his biological parents. He set off from Corinth to Thebes, and whether on the road or once he's already reached the city (all Greek myths have roughly 2-5 different versions), he ends up murdering Laius and, having solved the Sphinx's riddle, is named King of Thebes and marries his biological mother, Jocasta. Things seemed to be going pretty well for a while, but eventually Jocasta discovers the truth (not before they've had four children together) and kills herself. Then Oedipus blinds himself and is sent into exile. So, yeah, let's just say that Tyrion's patricide probably can't turn out that poorly.
2. Tukulti-Ninurta I and Ashur-nadin-apli
As the story goes, Tukulti-Ninurta I became the first native Mesopotamian to rule Babylon by defeating Kashtiliash IV in the 13th century B.C.E. Unfortunately for him, his sons didn't seem too impressed with that accomplishment and laid siege to his new, self-titled capital city, Kar-Tukulti-Ninurta shortly after its founding. Ninurta I was killed during the siege and it is believed that his son, Ashur-nadin-apli, took the throne. With this having happened more than 3,200 years ago, the specifics beyond that are a little murky.
3. Beatrice Cenci and Francesco Cenci
This might go without saying, but patricide need not be committed by a son. (In fact, if Tyrion hadn't gotten the job done last night, it wouldn't have been too shocking to see Cersei carry out the act herself.) Perhaps the most infamous incident of daughter-father patricide occurred in Rome in the last 16th century. Count Francesco Cenci was, by any and all metrics, a terrible dad. Not only was he frequently accused of violence and corruption, but he also kept his daughter, Beatrice and second wife, Lucrezia, as slaves in his castle, allegedly subjecting them to frequent brutality and sexual abuse.
One day, Beatrice decided she'd had enough and, along with her mother and brothers, orchestrated a plot to kill the Cenci patriarch. Two vassals — one of whom was rumored to be Beatrice's paramour — drugged Francesco and then bludgeoned him to death before throwing him off a balcony to make it look like an accident. (Alternate versions of the story say the vassals simply did the drugging and then the Cencis took care of the hammering). Even without a crackerjack CSI crew or DNA technology, Roman authorities quickly figured out this was murder, and executed all of the conspirators -- including Beatrice, who was beheaded at the age of 22. We'll have to wait another year to see whether a similar fate befalls the Lannister children.
4. Tekle Haymanot I and Iyasu I
Iyasu I reigned as Emperor of Ethiopia for 24 years from 1682 to 1706, when he abdicated the throne in favor of his son, Tekle Haymanot I. As it turned out, not everyone was on board with the decision, so Haymanot decided he had to murder his father, who had reportedly retired to an island in Lake Tana, to consolidate power. The choice to murder a revered former emperor turned out not to be a particularly popular one, and his father's courtiers took revenge and stabbed Haymanot I to death just two years into the young king's reign. Somehow it doesn't quite seem right that anyone would care to avenge Tywin's death with such vigor, but Tyrion might want to watch his back just in case.
5. Dipendra Bir Bikram Shah Dev and Birenda Bir Bikram Shah Dev
The most recent example of royal patricide isn't so much patricide as it was parricide. The Nepalese royal massacre took place on June 1, 2001, and it is believed that Dipendra murdered nine members of the royal family (including his father) with an arsenal of firearms before turning a gun on himself. The most common theory behind the murders is that Dipendra was angry about not being allowed to marry the bride of his choosing. Dipendra was named the 13th King of Nepal for three days while in a coma, before dying on June 4, 2001.