Theodor Capidan (April 28 [O.S. April 15] 1879 – September 1, 1953) was an Ottoman-born Romanian linguist. An ethnic Aromanian from the Macedonia region, he studied at Leipzig before teaching school at Thessaloniki. Following the creation of Greater Romania at the end of World War I, Capidan followed his friend Sextil Pușcariu to the Transylvanian capital Cluj, where he spent nearly two decades, the most productive part of his career. He then taught in Bucharest for a further ten years and was marginalized late in life under the nascent communist regime. Capidan's major contributions involve studies of the Aromanians and the Megleno-Romanians, as well as their respective languages. His research extended to reciprocal influences between Romanian and the surrounding Slavic languages, the Eastern Romance substratum and the Balkan sprachbund, as well as toponymy. He made a significant contribution to projects for a Romanian-language dictionary and atlas.