Michele Angelo Besso (Riesbach, May 25, 1873 – March 15, 1955 in Genova) was a Swiss/Italian engineer, and a close friend of Albert Einstein during his years at the Federal Polytechnic Institute in Zurich Einstein called Besso "the best sounding board in Europe" for scientific ideas.

Einstein and Besso: the Eagle and the Sparrow
Einstein's historic 1905 paper "On the Electrodynamics of Moving Bodies" in which the theory now known as special relativity was announced, was unusual for a scientific paper in that it carried none of the usual references to the literature of theoretical physics. The only individual credited with any contribution to the 1905 paper was Michele Angelo Besso, whom Einstein thanked for "many useful suggestions." Besso, whom Einstein once characterized as a perpetual student, had studied mechanical engineering at the Zurich Polytechnic during the years Einstein was enrolled in the physics section. The two met at a musical evening in Zurich and remained lifelong friends. Einstein had been boarding with the Winteler family in Switerland. The Winteler's daughter, Marie, was Einstein's first love; Einstein's sister Maja would eventually marry Winteler's son Paul; and his close friend Michele Besso would marry their eldest daughter, Anna.
In 1904, on the recommendation of Einstein, Besso took a position at the Swiss Patent Office. Whenever they could, the two friends engaged in long discussions of physics and mathematics. Besso played a very important role as a "sounding board" for Einstein, and when Einstein moved to Zurich and later Berlin, the two men visited and kept up a lively correspondence. When, shortly after taking up his position in Berlin in 1914, Einstein sent his wife Mileva and his sons Hans-Albert and Eduard back to Zurich, Besso and his wife, Anna Besso-Winteler, took on the role of intermediary between the feuding partners as their marriage was dissolving. They even cared for the couple's two sons during Mileva's illness. In 1913, when Einstein and Besso collaborated on the calculations in the manuscript under discussion here, Besso was living in Gorizia, near Trieste. The manuscript shows that in this case Besso functioned as considerably more than just a sounding board. Although he left the hardest parts to Einstein, he did take responsibility for some important parts of the calculations. In later years, Besso described his scientific collaboration with Einstein with a charming simile: Einstein was an eagle, and he, Besso, a sparrow. Under the eagle's wing, the sparrow had been able to fly higher than on its own.
Toward the end of his life, Einstein got a letter from the wife of his friend Michele Besso, who stayed in Switzerland. And she said, "You know, you and Michele were friends in Bern, and Michele is so talented, how come he never accomplished anything?" And Einstein said, "But of course, it's because he's a good man!" Einstein considered that his two marriages had been failures and looked at Michele Besso with his wife, and saw that they were very much in love.
Besso was of Jewish Italian (Sephardi) descent.