Bait (who had originally been named something else) was a soldier who was part of a troop of Malazan mercenaries under the leadership of "Cap'n" Yusen. This band of mercenaries gave every sign of being composed of experienced veterans of one of the various Imperial Malazan Armies.
The most recent contract taken by Bait and the rest of the mercenary troop had brought the mercs to the Isle of Jacuruku. Subsequent events found the band forced to enter and then travel through the extremely hostile environment of the Jungle of Himatan in search of a way off of the island.
At one point in the mercenaries' increasingly difficult and dangerous trek, Bait had had occasion to put one of his hands into the shallows of a wide stream, which resulted in that hand being viciously attacked by "swarming biting fish" and it being very badly mauled. Because of this, the trooper was re-named Bait by his comrades.