Walder Rivers, called Bastard Walder, is a natural son of Lord Walder Frey and has a formidable reputation as a fighter. His arms are those of House Frey with colors reversed and a red bend sinister added to mark his bastardy. His son, Aemon, is a knight and appears to be trueborn given his arms.
Bastard Walder accompanied his half-brother Lame Lothar to Riverrun after Hoster Tully’s death to enter negotiations. He also lead the attack on the camps at the Red Wedding. Later he was part of the besieging force at Riverrun, and nearly came to blows with Lord Piper.