Konstantin Josef Jireček[a] (24 July 1854 – 10 January 1918) was an Austro-Hungarian Czech historian, politician, diplomat, and Slavist.

[3] During his education, he became very interested in and studied several foreign languages (French, Serbo-Croatian, Bulgarian, Italian, Russian, English, Hungarian, Turkish and Greek).

[3] At this time, his nearest friends included French historian Ernest Denis (1849–1921) and the sons of Bulgarian theatre director and actor Krastyo Pishurka.

[3] In 1874 he took a study trip to Croatia-Slavonia and Serbia, after which he published several essays on the history and traditions of the South Slavic countries.

After the end of the Russo-Turkish War (1877–1878), which saw the re-establishment of the Bulgarian state, he helped construct the administration, school system and economy in the newly founded Principality of Bulgaria.

In Bulgaria, Mount Jireček, the third highest peak of the Rila mountain range, as well as two villages, also bear his name.