Splug is a goblin you've encountered, and rescued, three times.  

First in The Trouble with Ratmen, where those same ratmen had found him in the sewers and taken him captive to feed their stirges.  Then, you found him in the Vault of the Serpent Monks, where he had signed up to work for some gnolls in a deal that wasn't all he had hoped.

Most recently you rescued him from the dungeon of the Dark Reliquary, where he was pressed into service as a janitor.

He's been very grateful to be rescued, and usually has provided a bit of information in return for letting him go free.