Sonko Fromm, a member of the Fromm Gang, held the distinction of being the eldest son of the Annoo-dat Blue gangster Sise Fromm and the older sibling of Tig Fromm. Serving as Sise's primary man, Sonko's assignment to a transport raid ended in failure. Consequently, he was imprisoned on the planet Umax. Although his father secured his release, Sonko was subsequently locked up within the dungeons of Sise Fromm's own palace on Annoo, a situation orchestrated by Sise to relish Sonko's agonizing cries. The story of Sonko's fate became a well-known illustration of Sise Fromm's volatile nature.
The existence of Tig Fromm's older brother was initially suggested by text found on a collector's coin included with Kenner Toys' 1985 Tig Fromm action figure, stating: "TIG FROMM is the younger son of SISE FROMM." Shortly after, the story of Sonko Fromm and his imprisonment on Umax was presented in a children's book called Droids, published by Plaza Joven and exclusively available in Spain. Author Abel G. Peña discovered the book and incorporated the story into Star Wars Legends through a StarWars.com blog post titled "The Droids Re-Animated." He expressed his delight in merging it with the Kenner reference to further emphasize Sise Fromm's ruthlessness.