The Irate Italian chef is an employee at Luigi's, acting as one of the chefs and, as implied by the nom de guerre, has a very short and volatile temper.
When Homer Simpson, at that time working as a food critic for the Springfield Shopper, proceeded to issue a very harsh criticism of Luigi's lasagna (specifically, sarcastically calling it okay while claiming "Lasagna" was Italian for "pile of puke" while shouting the translation to the owner, Luigi Risotto's face), the chef, having overheard Homer's cruel comment to his boss, got furious, rushed out of the backroom and screamed his intention to cut Homer up in retaliation, also cussing him out in Italian while making good of his threat by swiping his cleaver at him. His attack on Homer failed, though he did nevertheless succeed at cutting a bit of Homer's ear off.
He later participated at the A Taste of Springfield food tasting event, and waved his cleaver threateningly at Homer from his stall as a group of furious spectators were about to gang up on Homer and beat him up for ruining the festival and presumably other negative actions he did earlier, with it being implied the chef was far more successful at harming Homer as a result. It's unclear whether he was involved Luigi and the other restaurant owners' assassination attempt against Homer due to not being present during the planning process, though given his grudge against Homer was bordering murderous levels even before the assassination plot was formed, it is likely.
