Long ago Serka, born as Jagai, was originally from Umbar, and born to parents of Haradrim descent. Serka's younger brother, Warad, was taken by village clerics and delivered to Gondor as a hostage of peace, though Jagai tired to stop them.
Soon after Ward was taken away Jagai's village was raided by the Vanishing Sons mercenary company, who murdered Jagai's parents and most of the villagers, but took Jagai and two other children. The mercenaries raised them harshly, leading to the deaths of the other children, but Jagai was hardened and worked his way through the Easterlings' ranks as he grew, taking the name of Serka. Eventually, having gained the title of "The Unkillable", he became the Vanishing Sons' leader.
Some time later, Baranor of Minas Ithil came to Lithlad, seeking the assistance of the Vanishing Sons. Serka soon recognized Baranor as his long-lost brother Warad and welcomed him. Serka, at the insistence of Baranor, eventually agreed to help him in taking the fortress of Shindrâm, though they initially disagreed about the venture's feasibility. During the campaign, which involved taking the outposts surrounding the fortress, Serka was betrayed by Zhója, one of his subordinates, who sold him to the uruk Ûshak. Baranor rescued Serka, who, on returning to The Oasis, had Zhója fed to the were-wyrms.
The campaign would ultimately be a success, and the fortress was captured, with both Serka and Baranor surviving the attempt.