Short answers, pulled from the story.
Arnolfo di Cambio was a thirteenth-century Italian architect and sculptor born around 1240 in Colle Val d'Elsa, Tuscany. He is known for designing Florence Cathedral and the sixth city wall of Florence, for his signed funerary monuments in Rome and Orvieto, and for his role as chief assistant to Nicola Pisano before establishing his own workshops.
Arnolfo di Cambio designed the Cathedral Santa Maria del Fiore (begun 1296), the Palazzo Vecchio (1299), and the sixth city wall of Florence (1284-1333). He was documented as capomaestro, or Head of Works, for Florence Cathedral in 1300.
The tomb of Cardinal Guillaume de Braye, who died in 1282, is a signed wall tomb by Arnolfo di Cambio in the church of San Domenico in Orvieto. It includes an enthroned Madonna modeled on an ancient Roman statue of the goddess Abundantia, with the Madonna's tiara and jewels drawn from antique prototypes. The monument became a model for Gothic funerary art in Italy.
Arnolfo di Cambio was Nicola Pisano's chief assistant on the marble pulpit for Siena Cathedral, a project that ran from 1265 to 1268. He began taking independent commissions before the pulpit was completed, traveling to Rome in 1266-1267 to work for King Charles I of Anjou.
Dante almost certainly knew Arnolfo personally, having met him at Florence Cathedral no later than 1300 when Dante was prior of Florence. Scholars believe Dante made a discrete reference to Arnolfo in Cantos XI and XIII of Purgatorio by twice citing the Battle at Colle Val d'Elsa of 1269, the town where Arnolfo was born.
Arnolfo di Cambio produced two major ciboria in Rome influenced by Cosmatesque art: the ciborium for Saint Paul Outside the Walls, completed in 1285 and signed "Arnolfus cum suo socio Petro," and the ciborium for Santa Cecilia in Trastevere, where he worked in 1293. Both feature intarsia and polychrome glass decoration.