Karl Theodor Robert Luther (April 16, 1822 – February 15, 1900), normally published as Robert Luther, was a German astronomer. While working at the Bilk Observatory in Düsseldorf, Germany, he searched for asteroids and discovered 24 of them between 1852 and 1890.
Two of his discoveries are now known to have unusual properties: 90 Antiope, a binary asteroid with equal components, and the extremely slow-rotating 288 Glauke. The asteroid 1303 Luthera and the lunar crater Luther were named in his honour. He was awarded the Lalande Prize in 1852, 1855, 1860, and 1861.