Flith was Riftun's lieutenant and second-in-command of the Ratguard. He enjoyed taunting the slaves, though, more often than not, the slaves ended up taunting him, as he was a rather dull-witted beast. During the escape of Triss, Shogg and Welfo from Riftgard, Flith took command of the Ratguards chasing after them; and when the runaways' stolen ship ran aground on a sandbar, Flith himself charged into the water to try to finish them off.
Unfortunately for Flith, by the time he caught up with the ship, Triss and Shogg had freed it from the sandbar and were again sailing away. Shogg smashed the rat over the head with an oar to keep him from following, knocking him unconscious and most likely killing him. It is unknown if he died immediately after the blow to the head, but if not, he was almost certainly drowned as his body was pulled out in the wake of the escaping slaves' ship. Hydrad succeeded him as Riftun's deputy.
Not to be confused with Filthy.