The Base Sons are a now organised military force who defend the lives of both bastard-born and low-born individuals. Beginning as a small organised group, they have become an army throughout the third, fourth and fifth seasons. They are made base-born individuals and the Smallfolk, from all across the Seven Kingdoms. Their hidden base of operations is coined as the "Basefort"
The group was created after King Joffrey Baratheon had almost all of King Robert's bastard children killed. They were a small group during the War of the Five Kings, but began strengthening their numbers. They are allies with the Brotherhood without Banners. They claim to have the support of House Harrigon and many lesser houses in the Stormlands, Riverlands and the Reach. By the Red Wedding their numbers reached around 30,000, big enough to win many battles.
Joshua returns to the Eyrie to meet with Lysa Arryn and his half brother Sweetrobin. He begs Lysa the aid of the Vale to help them against their enemies. Lysa however scolds Joshua, telling him the knights of the Vale will fight and die for Sweetrobin, not the bastard son of Lord Arryn. When he returns to camp, he is greeted by two of Lord Walder Frey's bastards, Ryger Rivers and Ser Walvar Rivers. They tell Joshua of House Frey's involvement in the Red Wedding, and that their half brother Tylan Rivers is fighting against Edwyn Frey, Lord Frey's heir. He agrees to fight with them against the Frey's. On their way the Twins, they come across the Brotherhood without Banners. The Base Sons and the brotherhood enter into an alliance. In a strange move, the Base Sons begin making wedding pacts. Their leader Joshua Stone marries Rearna Hill.
The Base sons travel to the Riverlands, finally acting on their plans to avenge the red wedding. Their first victory against the Freys is during the Battle of Freymoor, where they fought the combined forces of House Erenford, House Charlton and House Leafrey. After the battle, they are able to capture Ser Arwood Frey and two of his sons, Androw and Alyn.
The base sons are still in open war against the Frey's, killing their men wherever they go. It comes as a relief when they hear that Lord Walder Frey was mysteriously killed, along with his sons Lothar and Black Walder.
Ethon tells Joshua that the Stormlands and Borderlands are planning to unite to fight against the Iron Throne. The base sons, travel south, heading through the Borderlands with the aid of Ethon.
- Ser Joshua Stone, a bastard of Lord Jon Arryn and leader of the Base Sons.
- Rearna Hill, bastard daughter of Ser Gregor Clegane. Wife of Joshua Stone and the mother of Jon Greystone.
- Brendon Rivers, a bastard son of Ryman Frey.
- Ser Wesson Rivers, a bastard son of House Blanetree.
- Ser Walvar Rivers, a bastard son of Lord Walder Frey. He joined the Base Sons after hearing his father had betrayed the Starks and Tullys.
- Ethon, an unacknowledged bastard son of Dyron Blackgard.
- Ryger Rivers, a bastard son of Lord Walder Frey. He joined the Base Sons after hearing his father had betrayed the Starks and Tullys.
- Jormon Snow, a bastard son of Lord Jon Umber.
- Ethon Stone, a bastard of House Sunderland.
- Ser Pharrel Waters, a bastard of House Thorne.
- Gomely Greensea, a blacksmith who witnessed the killing of one of King Robert's bastards.
- Lorrand Bellsey, a bastard son of King Robert Baratheon from the Riverlands.
- Noella Rivers, a bastard from the Riverlands and the wife of Lorrand Bellsey. She is currently with child.
- Ollas Stone, a bastard of House Hersy.
- Ser Desmor Stone, a bastard of House Nolliner
- Merry Waters, a bastard from the Crownlands
- Ser Anron Flowers, a bastard of House Orme.
- Harmon Snow, a bastard from the North
- Ser Dorrick Storm, a bastard of House Musgood
- Ammett Hill, a bastard from the Westerlands.
- Ser Waylar Waters, a bastard from the Crownlands.
- Dilron Rivers, a bastard from the Riverlands.
- Larris Snow, a bastard from the North.
- Orwen Flowers, a bastard from the Reach.
- Wyllam Hill, a bastard from the Westerlands.
- Liya Stone, a bastard from the Vale.
- Maygen Rivers, a bastard from the Riverlands.
- Edder Stone, a bastard from the Vale.
- Lucan Hill, a bastard from the Westerlands.
- Garner Rock, a bastard from the Borderlands.
- Derron Stone, a bastard from the Vale.
- Dylar Storm, a bastard from the Stormlands.
- Jarrad Storm, a bastard from the Stormlands.
- Olivar Hill, a bastard from the Westerlands.
- Daman Rock, a bastard from the Borderlands.
- Myle Snow, a bastard from the North.
- Tyron Storm, a bastard from the Stormlands.
- Theodal Storm, a bastard from the Stormlands.
- Derren Snow, a bastard from the North.
- Tavion Hill, a bastard from the Westerlands.
- Sarina Waters, a vigilante better known as "the Raven", the eldest bastard of King Robert Baratheon. She is not a full member of the Base Sons, but maintains a loose association with them.