Agop Dilaçar (Armenian: Յակոբ Մարթաեան [Hagop Martayan], Istanbul, May 22, 1895 – Istanbul, September 12, 1979) was a Turkish linguist who specialized in Turkic languages and the first Secretary General and head specialist of the Turkish Language Association.
Of Armenian descent, Agop Dilaçar was born in Istanbul as Hagop Martayan in 1895. He graduated from the Robert College in 1915. He was proficient in 22 languages, and in addition to Armenian and Turkish, he knew English, Greek, Spanish, Azerbaijani, Latin, German, Russian and Bulgarian. He worked as a lecturer of the English language at the Robert College, and of Ottoman Turkish and ancient East languages at Sofia University in Sofia, Bulgaria.
He was invited as a linguist on September 22, 1932 to the First Turkish Language Congress held in Dolmabahçe Palace supervised by Mustafa Kemal Atatürk, the founder and first president of the Republic of Turkey, together with two other linguists of Armenian ethnicity, İstepan Gurdikyan and Kevork Simkeşyan. He continued his work and research on the Turkish language as the head specialist and Secretary General of the newly founded Turkish Language Association in Ankara. Following the issue of the Law on Family Names in 1934, Atatürk suggested him the surname Dilaçar (literally meaning language opener), which he gladly accepted. Nevertheless, he continued to use the surname Martayan to sign his articles in the Armenian language.
He taught history and language at Ankara University between 1936 and 1951. He also was the head adviser of the Türk Ansiklopedisi (Turkish Encyclopedia), between 1942 and 1960. He held his position and continued his research in linguistics at the Turkish Language Association until his death on 12 September 1979, in Istanbul.
Concealment of Armenian descent after death
After his death in 1979, in a news coverage, the then only Turkish TV channel TRT concealed the first name "Agop", which would suggest an Armenian descent, and instead mentioned "A. Dilaçar", using only the initial of his forename together with his surname. TRT was criticized for this attitude and the question was raised, if one is ashamed to mention the full name of one of the most important scholars of the Turkish language and thus reveal his Armenian descent. 
- Les bases bio-psychologiques de la Theorie Güneş Dil (1936)
- Azeri Türkçesi (Azerbaijani Turkish), 1950
- 1500ամեակի խոհեր (Thoughts on the 1500th Anniversary), 1951
- Batı Türkçesi (Western Turkish), 1953
- Lehçelerin Yazılma Tarzı (Writing Style of Dialects)
- Türk Dil ve Lehçelerinin Tasnifi Meselesi (Classification Issue of the Turkish Languages and Dialects), 1954
- Աստուածաշունչը եւ աշխարհաբարը (The Bible and the Armenian Modern Language), 1956
- Devlet Dili Olarak Türkçe (Turkish as a State Language), 1962
- Wilhelm Thomsen ve Orhon Yazıtlarının Çözülüşü (Wilhelm Thomson and Encoding of the Orkhon Inscriptions), 1963
- Türk Diline Genel Bir Bakış (A General Look at the Turkish Language), 1964
- Türkiye'de Dil Özleşmesi (Language Purification in Turkey), 1965
- Dil, Diller ve Dilcilik (Language, Languages and Linguistics), 1968
- Kutadgu Bilig İncelemesi (Research of the Kutadgu Bilig), 1972
- Anadili İlkeleri ve Türkiye Dışındaki Uygulamalar (Native Language Principles and Applications Outside Turkey), 1978
- Յօդուածներ (Articles), 2000
- Համայնապատկեր հայ մշակոյթի (Panorama of the Armenian Culture), vol. I, 2004
- Համայնապատկեր հայ մշակոյթի (Panorama of the Armenian Culture), vol. II, 2005
- Turkish language
- Turkish Language Association
- Atatürk's Reforms
- Sun Language Theory
- Karamanoğlu Mehmet Bey
- (Armenian) "Հակոբ Դիլաչարը Աթաթուրքի մոտ երգեց Զորավար Անդրանիկի երգը." ("Hagop Dilachar Sang Commander Andranik's Song in Atatürk's Presence"). Bnaban. July 7, 2012. Retrieved July 14, 2012.
- Cem Özdemir: "Der Völkermord an den Armeniern und die deutsche Öffentlichkeit", Heinrich-Böll-Stiftung, panel discussion, Berlin, September 22, 2011
- Dr. Sarkis Adam: "Dilbilimci AGOP MARTAYAN-DİLAÇAR ın Ölümünün 30. Yıldönümü" (Turkish), HyeTert, September 20, 2009. Retrieved February 15, 2012
- İrfan Özfatura: "Dilimizi dilim dilim... Agop Dilaçar" (Turkish), Türkiye Gazetesi, April 3, 2011. Retrieved February 15, 2012
- "A Place in the Sun, in Turkey, Malgre Sangre", August 24, 2009. Retrieved February 15, 2012
- "Agop Dilacar" (Turkish), Nouvelles d'Arménie en Ligne, August 28, 2008. Retrieved February 15, 2012
- Yalçın Yusufoğlu: "Agop Martanyan Dilaçar" (Turkish), September 13, 2009. Retrieved February 15, 2012
- Dilaçar's biography (Turkish)