The Noble Houses of Westeros provide most of the main characters of Game of Thrones. Fans love to debate the rights and wrongs of their favorite family, but there are many more players in these continent-wide conflicts. The Starks and the Lannisters get all the attention, but the power of the silver trout has to count for something. House Tully might not be the mightiest, but they are the most agreeable.
There's just too much going on in Westeros for every character to get the spotlight. There are a fair few characters that fans feel could be excised from the main story. They certainly don't have room for more. This leaves some characters, events, and entire families out in the cold. Whether House Tully deserves a place in the sun remains to be seen, but they are the subject of one of the strangest jokes in the franchise.
How did House Tully attain power?
House Tully is one of the few noble families to hold territory without ever ruling as kings. Their dynasty dates back to the Age of Heroes, the long period of peace after the First Men signed treaties with the Children of the Forest. They served a local king called the Hammer of Justice before kneeling to an Andal invader. They pledged fealty to Armistead Vance, starting a long pattern of submitting to the mightiest person within reach. The Tully's were rewarded with land, where they constructed their ancestral castle, Rivverun. They protected against invaders by supporting various leaders, many of whom failed. House Tully attained its real place of prominence during Aegon the Conqueror's all-consuming rampage across Westeros. The Tullys abandoned any attempt to resist invasion, falling upon their favorite strategy of bending the knee.
House Tully were, again, rewarded for their natural submissiveness. They were granted dominion over the riverlands, a fertile and populous region they've held for at least a thousand years. They took part in the Dance of the Dragons. Elderly house patriarch Lord Grover Tully supported Aegon II. His grandson Elmo supported Rhaenyra. He defied his grandfather's orders, knowing the old man was too weak to stop him. Elmo led an army in service of Rhaenyra and won a decisive victory in her name. Grover died of old age, placing Elmo in charge of Rivverun. His reign lasted less than 50 days, as he died from bad water during a march to King's Landing. Elmo's sons, Kermit and Oscar, led a new army to King's Landing, nearly securing the throne for Rhaenyra. Of course, both claimants to the Iron Throne died before the Dance of the Dragons was over, so it was all for naught. Yes, every Tully alive during the Dance was named after a Muppet. Grover, Elmo, Kermit, and Oscar do little of substance, but their bizarre naming scheme must be read to be believed.
How strong was House Tully?
House Tully has exhibited significant military power in various historical eras. The Tullys were an important part of Robert's Rebellion. Lord Hoster Tully sought to make strategic marriages and strengthen his rule. He tried to marry off his war hero brother, Brynden, but he refused. Brynden would take the nickname Blackfish and oppose his brother for the rest of his life. Lord Hoster decided to support Robert Baratheon's claim to the throne after The Mad King killed Brandon Stark, the man his daughter Catelyn was meant to marry. He wedded Catelyn to Brandon's brother, Eddard, and married her sister, Lysa, to Jon Arryn. House Tully was instrumental in the Battle of the Trident, which spelled the beginning of the end for Aerys II Targaryen.
What happened to House Tully?
The Red Wedding changed many things in Westeros. Lord Walder Frey, a former vassal of House Tully, arranged the execution of Robb and Catelyn Stark. They took Lord Edmure Tully hostage. Ser Brynden the Blackfish escaped. For their aid in putting down the Northern Rebellion, House Frey was made the new Great House of the Riverlands. House Tully never recovered from this blow. Brynden led a siege on Riverrun, retaking it for House Tully. Unfortunately, the Lannisters stepped in and stole it back. Lord Edmure is allowed to escape with his life, but the Blackfish is killed. House Tully was defeated until revenge came for House Frey. Arya Stark, Catelyn's daughter and Robb's sister, trained as an assassin with the Faceless Men. She killed Walder Frey and poisoned almost every male heir of the family. The Tullys retook Riverrun without anyone breathing to oppose them.
The history of House Tully is marked by strategic surrenders, tense negotiations, and non-stop betrayal. Their go-to strategy for almost 1,000 years was to betray their vows as soon as a stronger noble came along. Their own vassal used the same strategy to nearly wipe them out. If it weren't for one vengeful assassin, the Tullys would've been the victims of their own plan. Of course, Arya is technically a Tully too. Maybe the lesson of House Tully is that every few generations, someone competent will come along. Their commitments to family, duty, and honor may be questionable, but the silver trout always seems to find its way back upstream.