Ulrich von Dornum (1465/66[1] - 12 March 1536) was a son of the East Frisian chieftain Sibet Attena and his second wife Margarete von Westerwolde.

[1] His inheritance in Harlingerland, which his father had left in his will, was withheld from him by his older half brother Hero Oomkens.

Since their marriage had remained childless, her inheritance reverted to the House of Oldersum.

The transcript of the Oldersum Colloquy, which he wrote, was printed by Nikolaus Schirlentz in Wittenberg that same year.

By distributing this document, Ulrich von Dornum made a decisive contribution to the widespread spread and rapid implementation of the Reformation in East Frisia.