Demeter; died after 1254) was a Hungarian baron, who held secular positions during the reign of kings Andrew II and Béla IV.

Demetrius I belonged to the Ugod branch of Csák clan as the son of Luka.

[7] Prior to 1225, Demetrius was granted the royal castle of Németújvár (present-day Güssing in Austria) by Andrew II.

It is plausible that Demetrius acquired the fort, when he served as ispán of Vas County, where the castle located.

The Pannonhalma Archabbey, which once possessed Küszén Abbey, the short-lived predecessor of the castle, continuously petitioned against Andrew's decision to the Holy See, who urged Demetrius several times to recover Németújvár to the Benedictine friars, but he refused to do that.