Before the events of Pirate101, Captain Gunn was an average pirate smuggler- he was often the bane of every Marleybonian privateer and Monquistan prince (also, though it was never specified when, it is known that he won a piece of the Map to El Dorado off of Catbeard). That would all change when he journeyed to MooShu and met the Emperor. It was during his stay in Mooshu that Gunn discovered the Yum-Yum Fruit, which was capable of curing diseases, reversing age, increasing strength and making a person's breath minty fresh.
Unfortunately, the Emperor of Mooshu held Yum-Yum Fruit in high regard and, to ensure that only those of royal blood would consume it, the Emperor threatened anyone who wasn't royalty that ate the fruit with death by Ninja Pigs. Regardless, Captain Gunn loaded his ship full of Yum-Yum Fruit and spirited it away to Skull Island. He then began to make all sorts of Yum-Yum Fruit-based goods: Yum cake, Yum bread, Yum pudding and especially the ever-famous drink Yum! Pirates went crazy for the stuff! They loved it so much that Gunn even trade-marked the catchphrase "Yo-ho-ho and a bottle of Yum" so that, everytime someone says it, Gunn literally makes a penny. Gunn became one of the wealthiest pirates in the Spiral!
Alas, all good things must come to an end, and of course, Gunn was no exception. The Ninja Pigs eventually tracked him down and killed him in his tomb. His treasure and tomb went missing for years; however, one clue- Gunn's Will -was the key to finding his lost treasure.
Captain Gunn is dead by the start of Pirate101, the player receives a quest from Captain Avery to locate Gunn's tomb. All that Avery asks of the player in return is for them to claim one treasure- the Monkey Chalice, a golden chalice from Monquista. In exchange for this treasure, the player will receive a ship of their own.
However, getting to the treasure is easier said then done; Ratbeard (the main antagonist of the first world) quickly steal's Gunn's Will, running off with his rodent colleagues and leading the player on a mad chase throughout the better part of Skull Island. After many trials, the player reaches the island where Gunn buried the gold; unfortunately, Water Moles in the employ of Ratbeard stole all the treasure. The player learns from the undead Captain Gunn (courtesy of Old Scratch and his revival skills) that the Water Moles were from Waponi Wu, a very dangerous volcano. The player rushes off to claim the treasure, only to find that the Water Moles betrayed Ratbeard and have thrown most of the treasure into the volcano to please some fire god. Despite the degradation of most of the treasure, a tidy sum of over 500 gold coins and the Monkey Chalice are still in place. Though Gunn's gold will never be recovered in full, the fact that the Chalice is safe should be good enough- particularly because of what covers it...