Giselher was the grim, black-haired and lanky ringleader of the Rats. Prior to joining the Rats, he had been press-ganged into the local army and subsequently deserted, becoming part of a separate gang before meeting Iskra and founding the Rats. He was Iskra's lover. The entire gang, with the exception of Ciri, was killed at the hands of Leo Bonhart in Jealousy.
Giselher looked back, straightened his scarlet headband, and rested his gaze on Ciri. His face and its expression somewhat resembled Kayleigh's; the same malevolent grimace, the same narrowed eyes, the thin, protruding lower jaw. He was older than the fair haired Rat, though, and the bluish shadow on his cheeks was evidence that he was already shaving.
Giselher had deserted from the army. It was probably the army of the lord of Gheso who had allied himself with the insurgents from Ebbing. Probably. Giselher didn't actually know where the press gang had dragged him to. He had been dead drunk at the time. When he sobered up and received his first thrashing from the drill sergeant, he ran away. At first, he wandered around by himself, but after the Nilfgaardians crushed the insurrectionary confederation the forests were awash with other deserters and fugitives. The fugitives quickly formed up into gangs. Giselher joined one of them.