Don't look him straight in the eyes. He'll eat you alive! Careful how you talk to him; he's easily annoyed. Murky Pat is a pirate aboard the Lady Zay and the brother of Murky Matt.
When questioned about the feast he attended on
Lunar Isle during the quest Lunar Diplomacy, he claims to have a very rare medical condition that causes him to silent and immobile when he becomes drunk until he sobers up, and as a result is listed in "medical books". 
After you complete the quest
Lunar Diplomacy, Matt will talk about Pat and his mention of the player when asked what a pirate is doing in the  Grand Exchange.
Murky Pat also acts as a distraction in the
Livid Farm, where he may occasionally teleport in and ask players to cast Vengeance Other on him, based on a specific target.
Murky Matt, RuneScape. "Then ye must know me brother! Murky Pat!"
Murky Pat, " Lunar Diplomacy", RuneScape. "When I'm drunk I become completely silent and immobile, and just sit quietly by myself until I have sobered up."
Murky Pat, " Lunar Diplomacy", RuneScape. "Oh absolutely. I'm in the medical books and everything." ^
Murky Matt, RuneScape. "Well, 'e be on that ship for sure. And I remember 'im tellin' me about some guy like ye, getting all mixed up with curses and cabin boys."