Friedrich Wilhelm Bessel

German astronomer and mathematician, started out as an apprentice of a trade company, studying astronomy on his own in his spare time, later became assistant at a small private observatory, and finally director of the new Konigsberg observatory. There, he observed more than 75,000 stars up to magnitude 9, computed the first precise value for the precession constant and he made the first significative evaluations of parallaxes. He also was one of the firsts to believe in the existance of Sirius and Procyon's companions. His paper on the Bessel functions is dated from 1824 but was published in 1826.

Sources: Advanced Engineering Mathematics, Erwin Kreyszig; also, Le Petit Robert 2.