The bartender at the Blue Moon Inn in Varrock is a man who sells drinks to people. He has a son named Balek. Despite his son's claims, he does not own the tavern but just works for the innkeeper.
The bartender is also involved in the simpleTreasure Trails clue "Speak to the bartender of the Blue Moon Inn in Varrock."
During the Bar Crawl miniquest, he is one of the bartenders that you must get a drink from. His drink is the "Uncle Humphry's Gutrot". It costs 50 coins and lowers Attack, Defence, Strength, and Smithing, doing up to 20 life points. It also makes you throw up. The drink can only be purchased during the Bar Crawl.
The bartender also seems to be one of the few NPCs who are aware that RuneScape is a "computer game". This is an example of a character "breaking the fourth wall". When players inquire what the bartender means by this, he makes a brief attempt at explaining what a computer is, calling it a "magic box". However, the player is baffled, and calls the bartender's idea "obviously mad".