(Warning: This post contains spoilers for Seasons 1-5 of Game of Thrones. Read at your peril.)
First, a disclaimer: if you really want to comprehend Game of Thrones, there is no substitute for watching Game of Thrones. It's so complex, with so many characters and plots and shifting allegiances, that trying to process all the information just from reading about it without seeing the faces associated with the names is a nearly impossible task. Even people who watch the show every week have to do a little homework now and then to jog their memories or clarify something. Plus it's a great show, packed with terrific performances, impeccably crafted costumes and production design and special effects, stirring action and deliciously articulated dialogue. You're doing yourself a disservice by missing out.
But obviously, with Season 6 premiering on April 24, unless you're an unemployed insomniac there's not enough time to watch all 50 episodes. So this primer will give you the big stuff — major characters and history through the first five seasons-- that you'll need to know to have a working understanding of what you're watching. For more detail specifically pertaining to Season 6, read TVGuide.com's guide to where Game of Thrones left off in Season 5. For a quick rundown of the show's biggest moments, check out the "most shocking moments" gallery.
What it's about
The central question of Game of Thrones is "who will be the monarch?" Before the events of the show, there was a war known as Robert's Rebellion, where Robert Baratheon (Mark Addy) overthrew the "Mad King" Aerys Targaryen and became King of the Seven Kingdoms of Westeros. After Robert's death in Season 1, his son Joffrey (Jack Gleeson) took his seat on the Iron Throne. Joffrey was killed in Season 4, and his brother Tommen (Dean-Charles Chapman) is presently the King. However, since Joffrey and Tommen are not actually Robert's biological sons — they and their sister Myrcella (Nell Tiger-Free) are products of an incestuous affair between Robert's wife Cersei Lannister (Lena Headey) and her twin brother Jaime (Nikolaj Coster-Waldau), the worst-kept secret in Westeros — their claim to the throne is disputed. Since the Baratheons are just boys, the real power belongs to the elder Lannisters, particularly Cersei and her father Tywin (Charles Dance), at least until Tywin's death in Season 4.
Watch the throne
The primary contender is Daenerys Targaryen (Emilia Clarke), the daughter of Aerys. Daenerys, who was not yet born during Robert's Rebellion, grew up in exile outside of Westeros. She has a very strong claim to the throne, both for her regal bloodline — Targaryens, of which she is the last, ruled Westeros for centuries before Robert Baratheon took over — and for her temperament, which is the right combination of just and strong. She also has three dragons, the Game of Thrones equivalent of the atom bomb. For the length of the show, she has been gathering an army on the Eastern continent of Essos to eventually attack the capital city of King's Landing and install herself as ruler. She started the show by getting wed to Khal Drogo (Jason Momoa), the leader of a Dothraki tribe, which earned her the title Khaleesi, or queen. Drogo died, and since then she has been traveling all over Essos, taking over cities, freeing slaves, gathering support, and learning how to rule through trial and error. She commands the Unsullied, an army of super-soldiers she freed from slavery, and the Second Sons, a mercenary outfit. She has conquered the cities of Astapor, Yunkai and Meereen. At the end of Season 5, Meereenese rebels tried to assassinate her, but she escaped on the back of Drogon, her most powerful dragon, only to be captured by Dothraki riders, who are probably from a rival tribe to the one of which she is Khaeleesi.
About her enemies...
Back in Westeros, the other contenders for the throne are mostly dead now. Stannis Baratheon (Stephen Dillane), Robert's brother, died in the Season 5 finale. Stannis was a formidable warrior who would have been a decent king, but he was undone by religious fundamentalism and tactical missteps.
Robert and Stannis' youngest brother, Renly (Gethin Anthony), also claimed the Iron Throne, but he was killed in Season 2 by a shadow-creature summoned by Stannis and his spiritual advisor, Red Priestess Melisandre (Carice van Houten).
In the North of Westeros, Robb Stark (Richard Madden), the eldest son of Eddard "Ned" Stark (more on him in a minute), renounced the Iron Throne and declared himself "King in the North," going to war with the Lannister army to gain independence. Robb and his mother Catelyn (Michelle Fairley) were killed in the infamous Red Wedding, where they were betrayed by the Freys and the Boltons, other Northern families, who made a deal with Tywin Lannister to sell out the Starks in exchange for control of the North.
Meet our heroes
The Starks are pretty much the heroes of Game of Thrones. Ned (Sean Bean), the Stark patriarch, was the star of Season 1, but he was executed on Joffrey's orders after he challenged Joffrey's legitimacy. After that, his children were scattered and have each been having their own adventures. The eldest surviving full-blooded Stark is Sansa (Sophie Turner), who keeps getting married off to different men for strategy reasons — first Joffrey, then Tyrion Lannister (Peter Dinklage), then Ramsay Bolton (Iwan Rheon). Sansa started the series as a very naïve girl, but her cruel circumstances have forced her to become a tough and cunning survivor. Her younger sister, Arya (Maisie Williams), was always tough and cunning, and she has become a vengeance-fueled killer on her journey, which has been conducted mostly in secret. None of her surviving family members know where she is or whether she's even alive. She's currently in the Essos city of Braavos, studying to be an anonymous assassin, but she's been struck blind as punishment for a forbidden act of revenge. The two youngest Starks are Bran (Isaac Hempstead-Wright) and Rickon (Art Parkinson). Bran was pushed out of a window by Jaime Lannister in the series premiere, which put him into a coma. When he came out of it, he could no longer walk, but he did have psychic powers. He can take over the bodies of other creatures, an act called "warging," and has oracular visions. He's been developing his powers under the tutelage of a man called the Three-Eyed Raven (Max Von Sydow). Rickon, the youngest, is just a little boy, but he will have a larger part than ever before in Season 6. Bran and Rickon are presumed dead by most people, and Sansa is the only surviving Stark who knows they're alive, but she doesn't know where they are.
There's also a Stark half-brother, Jon Snow (Kit Harington). Jon is the bastard son of Ned Stark and a tavern wench. Since Catelyn Stark is not his mother, he does not get the Stark name or full noble privilege, but he has the Stark traits of honor and courage. He served in a defense order called the Night's Watch, which patrols the border of Westeros and the lawless lands to the north, rising to the rank of commander. Jon developed friendly relationships with people who live north of the wall that separates Westeros from the northlands, which angered other members of the Night's Watch, who betrayed and murdered him. When Season 6 begins, Jon Snow will be dead, but he will probably be resurrected somehow, because along with Daenerys Targaryen he's the show's most narratively important character.
Trouble beyond the wall
While this fight over the throne is going on, there's a bigger problem developing north of the Wall: White Walkers, a legendary race of mythical humanoid demons, have reemerged after an 8000-year absence. White Walkers are incredibly powerful, capable of reanimating dead bodies into beings called "wights" to do their bidding. They can only be killed with weapons made from certain materials, which are still being figured out. Jon Snow killed one with his sword made of Valyrian steel. They are a much bigger threat than any human, but people in the south don't take them seriously, and the undermanned, fractured Night's Watch is currently the only line of defense against them.
The royal family
Besides the Starks, the most important family is the Lannisters: Cersei, Jaime and Tyrion. Cersei is Robert Baratheon's widow and the mother of King Tommen. As the Queen Mother, she has a lot of power and influence, but not as much as she'd like. She's a harsh and arrogant woman who was finally humbled in Season 5, when a plan to reassert her control in King's Landing backfired and she was humiliated in front of her subjects. Her twin brother is Jaime, who is also her incestuous lover and secret father of her children. He is a knight and tremendous fighter, at least until he lost his sword-hand. Jaime is not all bad — he's a killer and a Lannister, but he is not needlessly violent, and he will save people he feels responsible for, like his younger brother Tyrion. Tyrion is a dwarf, a drunk and a brilliant strategist. His family except Jaime always hated him, and he's since left the Lannister fold entirely after murdering his father Tywin. After fleeing King's Landing, he linked up with Daenerys Targaryen, and he's holding down the fort in Meereen in her absence.
There are dozens of other important characters, like all-knowing Varys (Conleith Hill), conniving Petyr "Littlefinger" Baelish (Aidan Gillen) and loyal Davos Seeworth (Liam Cunningham), and numerous other families and locations, like the Martells in Dorne and the Greyjoys in the Iron Islands and the Tyrells in the Reach. You'll be able to piece together who they all are once you get into the show. If you can, watch with a buddy who knows the show who can explain the finer points to you.
It's a lot to take in, but it'll all be worth it when something terrible happens and you have a visceral emotional reaction. Happy Gaming.