Luigi Risotto, real name Lothar Folkman is the proprietor of Luigi's.
A cooking prodigy, Lothar Folkman opened his Italian restaurant in Springfield to critical success, but empty seats. No one wanted to eat Italian food prepared by someone named Lothar. But after making a fake Italian accent, changing his name, and getting a makeover, his eatery became packed almost every night. Unfortunately, the charade has driven Luigi into a love/hate relationship with his customers that occasionally bubbles to the surface like tomato sauce in a pot that's one size too small.
Luigi owns an Italian restaurant in Springfield, that serves average Italian food. Luigi often treats his customers rudely, insulting and belittling them (such as calling Bart “the ugly kid”); at times under his breath, at other times in a conversational tone, and sometimes shouting the slurs to the (unseen) chef Salvatore (”Hey, Salvatore! Give the ugly kid a plate of the red crap!”). Luigi seems to have some connections to the mafia. Local gangster Fat Tony is a frequent customer at his restaurant, despite the fact that he was one of the targets of Fat Tony's plan to get rid of all other food retailers except Marge's. He does not actually speak Italian, only "fractured English" with a strong Italian accent, as did his parents. He says the phrase, "I guarantee," a lot.
When Homer was a food critic, he gave Luigi's eatery a poor review; in retaliation, Luigi hired a friend to place a horse's head in Homer's bed (a reference to The Godfather). Homer subsequently ate the head and gave it a bad review.
His one on-screen companion is Giuseppe the monkey.
He can play accordion.
In The Simpsons: Tapped Out (app for Android and iOS), Luigi has a slip of his tongue and reveals his true accent is British. He quickly realizes his mistake and returns to his Italian. He also reveals that his mother died from getting her mustache caught in a dough mixer.
Behind the Laughter
Luigi is a parody of the "Italian pasta/pizza chef" stereotype, but seems to be aware of his status as a stock character. His surname is a reference to the Italian food risotto. He also seems to be a parody of Tony from Lady and the Tramp and also sounds like Mario and Luigi of Super Mario Brothers.