was Vanni Fucci from The divine Comedy a real person and if so, what did he do?

Answer 1

Yes, he was:
"Under the escort of his faithful master, Dante not without difficulty makes his way out of the sixth gulf; and in the seventh, see the robbers tormented by venomous and pestilent serpents. The soul of Vanni Fucci, who had pillaged the sacristy of Saint James in Pistola, predicts some calamities that impended over that city, and over the Florentines."

"Vanni Fucci: Nicknamed Bestia, for his brutality, he was the Illegitimate son of Fuccio de' Lazzari. He took part in the vicious struggles that divided his city Pistoia, siding with the Black Guelphs, repeatedly sacked the houses of his political enemies. In 1293, he stole the reliquary of San Jacopo from the sacristy of the Cathedral of Pistoia, for which crime the innocent Rampino Foresi was arrested and nearly executed, before the guilt of Fucci and his accomplices was discovered.
Among the thieves, like the mythical phoenix, he is burned to ashes and restored. Inf. XXIV, 97–118.
Refers to himself as a "mule" meaning "bastard" ("mul ch'i' fui"). Inf. XXIV, 125.
Prophesies the triumph in Florence of the Black Guelphs over the Whites. Inf. XXIV, 143–151.
Swears against God while performing an obscene gesture (a "fig", the insertion of a thumb between the first and second fingers of a closed fist). Inf. XXV, 1–18."