Matthew Csák III (of Trenčín) (Matúš Čák III (Trenčiansky), Chak, Chaak, Czak; in (modern) Hungarian Csák Máté) (about 1260 – 1321) was the ruler of the Váh and the Tatras region, and lived in Trenčín castle in Slovakia.

Although never being an official king of Slovakia, he – as a very rich and influential Hungarian magnate – de-facto became the ruler of what is today Slovakia at the beginning of the 14th century. He owned 14 counties and 50 castles and fortresses in the region of present day central and western Slovakia, had an own army and was conferring the same degrees and functions as are awarded by the Hungarian king.

After his defeat in the battle near Rozhanovce (at the river Torysa) in 1312, where his army fought against the troops of King Charles Robert of Anjou, his influence started to decrease and his "empire" ceased when he died in 1321 in Trencin.