Wikipedia
Býleistr
Býleistr ('calming-lightning', sometimes anglicised Byleist) is the brother of Loki in Norse mythology.
Nothing is known about him apart from this kinship. Snorri Sturluson states in his Gylfaginning (34) that "[Loki]'s brothers are Býleistr and Helblindi", and several Eddic texts use the Loki- kenning "brother of Býleistr" (bróðir Býleists) ( Völuspá, 51; Hyndluljóð, 40; Skáldskaparmál, 16).
Though not directly attested in any original source, scholars have considered Býleistr to be a son of Fárbauti and his consort Laufey, because they are mentioned as Loki's brothers. However, their exact role in the ancient mythic complex surrounding Loki's family remains unclear.