Arthur is one of the titular characters in "The One With The Bullies".
Ross and Chandler encounter him and his friend Carl for the first time after accidentally stealing their seats while in the coffee shop. Despite the muscular, powerful build of Arthur and Carl, Chandler (most likely because of their formal, smart, and well-dressed appearances in suits and ties) feels comfortable enough in their presence to make a joke regarding the incident, but Arthur and Carl seem to get the impression that he is mocking them, so Arthur steals his hat in retaliation. Although initially frightened, Ross and Chandler later decide to confront them despite doubting their ability to win a fight with the two more physically imposing men. However, while they and the two now more casually dressed bullies are discussing the rules for the fight, Ross and Chandler notice some wannabe thieves making off with the valuables they had set aside for the fight and give chase. Ironically, the four men end up joining forces to chase down and fight off the would-be thieves, and they bury the hatchet.