SAN FRANCISCO — He wears sunglasses in the dark, talks about himself in the third person and has a bodybuilder’s physique, but the minor character infiltrating this year’s World Series wears the uniform of neither the Kansas City Royals nor the San Francisco Giants. Duffman, an animated figure from “The Simpsons,” is the alter ego of the Giants rookie Matt Duffy, who has covered the knob of his bats with decals of the cartoon character as a caped cleanup hitter.

In Game 4 on Saturday night, Duffy wielded his bat like a tourniquet and helped stanch the Giants’ bleeding. After the Royals scored four runs in the top of the third to take a 4-1 lead, Duffy, hitting for reliever Jean Machi, singled and scored on a Buster Posey single to begin the Giants’ 11-4 comeback victory to even the Series at two games each.

Duffman, the faux beer pitchman with the big muscles, and Duffy, the real-deal infielder with the scrawny body, were joined at the quip by a California sportswriter at The Long Beach Press-Telegram when Duffy was in high school.

The nickname stuck, so this year, while starring for the Class AA Richmond Flying Squirrels, Duffy ordered the Duffman decals. By the time they were shipped to him in early August, Duffy had been called up to the big leagues, and so the package traveled from Richmond to New York to Milwaukee to Kansas City, making more stops on the way to San Francisco than Duffy, a 2012 draft pick, actually did.