Guido Fubini was born in Venice in 1879. He was urged toward mathematics by his father, a teacher in a mechanics school. At age 19, he enrolled in the Scuola Normale Superiore in Pisa, where he obtained his mathematics doctorate in 1900 at age 21. His thesis, published in 1902, was in geometry.
Fubini's teaching career developed rapidly. He taught first at the University of Catania in Sicily, a bit later at the University of Genoa, and in 1908 he went to the University of Turin. During the First World War, he became engaged with military problems that led him to do applied mathematics and mathematical physics.
When the events that led to World War II were unfolding, Fubini had to consider what was best for his wife and two engineer sons. When the Institute for Advanced Study in Princeton offered him a position in 1939, he accepted and emigrated to the United States.
His worked in many areas of mathematics, but his most important research centered on what was called absolute differential calculus, now known as tensor analysis, which is a method of studying quantities that depend linearly on vectors. And of course you, and many others, know of him because of Fubini's theorem.
Already in poor health when he left Italy, he died after about four years in America.