He starts the Lumbridge and Draynor Tasks, with talking to him being one of the beginner tasks. He also gives you any item rewards that some of the Lumbridge and Draynor tasks provide. Once the beginner tasks are completed, players may talk to Explorer Jack to get the reward for the beginner tasks: His explorer ring, which can be used to regenerate run energy.
Jack featured briefly in the old tutorial, Unstable Foundations, where the player reached Lumbridge's surface by mining through a wall in Roddeck's enormous cellar, which led to Jacks, and then climbing up a ladder into his house. Roddeck explained that Jack is "an understanding chap; he won't mind us walking through his house," and indeed, Jack expressed a lack of concern and even amusement at the players explanation of what happened with Roddeck's pet dragon.
Jack is the start of the Myths of the White Lands quest, in which he asks the player to collect some "riches" from the Land of Snow, of which he was informed of by Marius, a passing Snow imp. He tells players to talk to an aquantice of his, a wizard named Isidor, in order to get to the Land of Snow.
After the player retrieves the "riches" from a Yeti lair, Marvin, Barry and Marius appear, telling the player that they were playing a prank on Jack, and the "riches" are in fact yeti dung. The player then has the choice of going on with the prank, or telling him the truth.
Either way, Jack takes the prank with good humour, and rewards the player regardless. If the player talks to Explorer Jack fifteen minutes later, he will reveal that he sold the stones to a passing witch, and gives you 5,000 coins as your share of the profit.
Jack's house was damaged heavily by Saradomin and Zamorak when they returned to Gielinor at the start of the Sixth Age, forcing him to flee his house, moments before it collapsed. He was then helped to his feet by his neighbor, Hank, whose house was also destroyed. Not wishing for the gods to beat him, made a cup of tea, and returned to his duties as taskmaster, continuing to do so as the Battle of Lumbridge raged on outside.
During the Lumbridge Rebuildathon, his house was repaired by Foreman George, his crew of builders, and the adventurers of Gielinor. During the repairs, he camped in a tent just outside his house, but has now returned inside. He rewarded those who assisted the builders in rebuilding his house with a replica of his helmet.
Explorer Jack's house, ruined as a result of the Battle of Lumbridge.