Nephthys
The Gr8est!!!!!!!!
The bounty hunter who shot and killed a Battlemaster was THE Bounty Hunter aka the player character Grand Champion of the Great Hunt.
As in, the same guy who defeated a Mandalore contestant after getting shot with a sniper 4 times, solo'd one of Vitiates massive Sithspawn that had slaughtered every Mandalorian sent after it, solo'd a Jedi Master and his apprentice at point blank range, solo'd a Jedi Strike team, blitzed a Jedi, decimated the Green Jedi, whooped a Sith on Dromund Kaas, shitstomped the GenoHaradan, defeated a Darth powerful enough to blitz other Darths and a host of other insane shit I've forgotten.
The Champ is one of the best non-force sensitives in history, easily up there with Boba and Jango Fett and GG.
Also it wasn't that Kas'im was underestimated, his abilities were made extremely clear in the novel, its just that Bane was better. 🙂