Hermann Joseph Klein (14 September 1844 – 1 July 1914) was a German astronomer, author and professor. Born in Cologne, Germany on 14 September 1844, he attained his doctorate from the University of Cologne in 1874, and taught at the school. He was a member of the Selenographic Society and the crater Klein on the Moon is now named after him. In 1878 he claimed to have discovered a new crater on the Moon near Hyginus.