Karamanoğlu Mehmet Bey (~1245–1277) is the most emblematic ruler of the beylik. In 1261 he took over the leadership of the principality after his father Karaman Bey. In 1277 he moved against Mongol influence over the Seljuk throne, seized Konya and placed Gıyâseddin Siyavuş, the son of İzzeddin Keykâvus II, on the Seljuk throne.
Mehmet Bey's most important step on the stage of history, however, was the ferman (decree) he issued the following day in Konya, on 13 May 1277. At that time Persian and Arabic were used at the Seljuk court and in state correspondence, while the people spoke Turkish. With this decree Mehmet Bey declared Turkish the language of the state.
"Şimden gerü hiç kimesne kapuda ve dîvânda ve mecâlis ve seyrânda Türkî dilinden gayrı dil söylemeyeler." — Karamanoğlu Mehmet Bey, 13 May 1277, Konya
"From now on no one shall speak any language other than Turkish at the palace, in the divan, in assemblies and in the public squares."
Mehmet Bey was able to remain in Konya for only 37 days. Forced to withdraw in the face of Mongol pressure, he fell as a martyr together with his brothers on 20 June 1277 in the battle he fought against Mongol forces at Kızıldağ. His grave is in the village of Balkusan, in the district of Ermenek.
Mehmet Bey's decree carries great symbolic value in Turkish cultural history. 13 May is commemorated in Türkiye as "Türk Dil Bayramı" (Turkish Language Day).